the university of hong kong curtain wall defects in … · the incidence and seriousness of curtain...

THE UNIVERSITY OF HONG KONG

CURTAIN WALL DEFECTS IN HONG KONG HIGH-RISE OFFICE

BUILDINGS – INCIDENCES, SERIOUSNESS AND CAUSES

A DISSERTATION SUBMITTED TO

FACULTY OF ARCHITECTURE

IN CANDIDACY FOR

THE DEGREE OF

BACHELOR OF SCIENCE IN SURVEYING

DEPARTMENT OF REAL ESTATE AND CONSTRUCTION

BY

MOOK KING TONG, CHRIS

APRIL 2006

HONG KONG

Declaration

I declare that this dissertation represents my own work, except where due acknowledge is made, and that it has not been previously included in a thesis, dissertation or report submitted to the University or to any other institution for a degree, diploma or other qualification. Signed : i Name : i Date : i

Abstract

Curtain wall has widely been installed as building envelope for many high-rise office

buildings. With advantages of good appearance, space saving, lightness and rapid

construction, curtain wall is very attractive to designers. However, the consequences of

curtain wall defects could be very serious. An example of serious curtain wall defects is

the shattering of hundreds of glass panels of buildings in Wan Chai by Typhoon York in

1999. To ensure the safety of curtain wall, causes of defects should be identified and

eliminated. Therefore, in this Study, the incidences, seriousness and causes of curtain wall

defect in Hong Kong high-rise office buildings are investigated. A survey is used to study

the incidence and seriousness of curtain wall defects, while face-to-face interviews with

Building Managers and site visits to buildings are held to find out the causes of curtain

wall defects. Curtain wall consultants and contractors are also asked to give

supplementary information on the causes of curtain wall defects. 20 defects items and 72

defects’ causes are identified and tested.

i

Acknowledgements

I would like to express my deepest gratitude to my supervisor, Dr. Richard Fellows, for

his valuable advice, continuous inspiration, support, patient guidance and encouragement

through the preparation of this dissertation. Without these, this dissertation would not

have been successfully completed.

Thanks should also be given to all people who have participated in the survey or the case

studies, including Mr. H. L. Leung, Mr. K. K. Pang, Mr. K. M. Lam, Mr. Tang W. Y.,

Mr. K. C. Tang, Mr. K. P. Wong, Dr. Y. S. Zhou, Mr. Wong, Mr. Leung, Mr. Chan and

Mr. T. T. Chan. Without their support, data collection for this dissertation would not

have been successfully completed.

My sincerely thanks should be given to my parents and friends for their continuous

support. Finally, I have to express my thanksgivings to God.

ii

Table of Contents Page Abstract i Acknowledgments ii Table of Contents iii List of Figures v List of Tables ix List of Photos xii Chapter 1 Introduction 1

1.1 Background 1.2 Aim 1.3 Objectives 1.4 Hypothesis 1.5 Methodology 1.6 Outline Approach

Chapter 2 Literature Review 9

2.1 Introduction 2.2 Definition of Terms 2.3 About Curtain Wall 2.4 Types and Seriousness of Curtain Wall defects 2.5 Causes of Defects 2.6 Conclusion

Chapter 3 Research Design 87

3.1 Introduction 3.2 Types of Research Methods 3.3 Use of Research Strategies in the Study 3.4 Data Collection 3.5 Data Analysis 3.6 Conclusion

Chapter 4 Survey Questionnaire 97

4.1 Introduction 4.2 Construction of the Survey Questionnaire 4.3 Possible Defects Identified from Previous Literature 4.4 The Relative Seriousness of Defect Items 4.5 Conclusion

iii

Chapter 5 Discussion of Survey Questionnaire Results 104

5.1 Introduction 5.2 Description of Sample 5.3 Results of Survey Questionnaire 5.4 Implications of the Results 5.5 Conclusion

Chapter 6 Case Study Questionnaire 118

6.1 Introduction 6.2 Construction of the Questionnaire 6.3 Possible Causes of Defects Identified from

Previous Literature 6.4 The Rating of Causes of Defects 6.5 Conclusion

Chapter 7 Case Study Findings Analysis and Discussions 126 7.1 Introduction 7.2 Case Study Design 7.3 Case Study Questionnaire Results Analysis

and Discussion 7.4 General Discussion of Case Study Questionnaire

Results 7.5 Conclusion

Chapter 8 Conclusion 165

8.1 Evaluation of the Results and Findings 8.2 Limitations of the Study 8.3 Recommendations of Further Investigation

Appendix (A) Performance Characterizes of Materials for 177

Curtain Walling (B) Design Wind Pressure 178

(C) Building Maintenance Decision Diagram 179 (D) Parameter used in Chew, et al (2004)’s Research 180

and their Weightings (E) Questionnaire Brief 181 (F) Survey Questionnaire 182 (G) Case Study Questionnaire 185 References 189

iv

List of Figures

PAGE

Fig. 2.3.1 A Typical “Stick System”………………………………………… 15

Fig. 2.3.2 A Typical “Panel System” ……………………………………….. 16

Fig. 2.3.3 Details of Single-stage Joints: a (i) Filled Joint and (ii) Gasket

joint………………………………………………………………..

21

Fig. 2.3.4 Details of a Drained Joint………………………………………… 22

Fig. 2.3.5 A Pressure Equalization System………………………………….. 24

Fig. 2.3.6a A Fixing System using Brackets and Halfen Channels…………... 25

Fig. 2.3.6b An Isometric view of Fixing System using Brackets and Halfen

Channels…………………………………………………………...

26

Fig. 2.3.7a A Fixing System for the Stick System using Brackets and Steel

Plates welded with Anchors………………………………………

26

Fig. 2.3.7b A Fixing System for the Unitized System using Brackets and

Steel Plates welded with Anchors (i) View form Above and (ii)

Lateral View……………………………………………………….

27

v

Fig. 2.3.8 (i) Aluminum Angles are used for Connecting Mullion and

Transom (ii) An Isometric View of an Aluminum Angle…………

28

Fig. 2.3.9 A Tenon Joint used for Connecting Mullion and Transom ……… 28

Fig. 2.3.10 Screws Directly Applied from Mullion Side into Transom’s

Screw Holes……………………………………………………….

29

Fig. 2.3.11a Triangular Beads used to Fix Glass Panels………………………. 30

Fig. 2.3.11b Square Beads used to Fix Glass Panels………………………….. 30

Fig. 2.3.12 Adaptors, Clamping Bars and screws used to Fix Glass Panels…. 31

Fig. 2.3.13a Aluminum Clamping used to Fix Metal Panels………………….. 32

Fig. 2.3.13b Details of Connection between Panels, aluminum Clamping and

Metal Mullion……………………………………………………

32

Fig. 2.3.13c Installation of UPVC Edge Profiles……………………………… 33

Fig. 2.3.14 Movements due to Moisture, Temperature, Creep and Differential

Settlement………………………………………………………….

37

vi

Fig. 2.3.15 An Example of Fastener – Fastener Fixing Mullion to the

Concrete Slab……………………………………………………..

46

Fig. 2.3.16 Welding of “T” Piece to the Mullion……………………………... 47

Fig. 2.3.17 Types of Maintenance ……………………………………………. 51

Fig. 2.4.1 Types of Sealant Failure………………………………………….. 60

Fig. 2.5.1 The Result of BRE’s Research - Origins of Building Faults ……. 64

Fig. 2.5.2 Causes of Curtain Wall Failures ………………………………….

65

Fig. 2.5.3 Composition of Chew’s Technical Evaluation Index……………. 66

Fig. 2.5.4 Moisture Moments from Floor to Floor without Flushing……….. 71

Fig. 2.5.5 Water Barrier between Floors…………………………………….. 72

Fig. 4.1 Weight of Each Factor used in the Calculation of Defects’

Seriousness………………………………………………………..

102

Fig. 5.1 Incidences of Curtain Wall Defects………………………………. 106

vii

Fig. 5.2 Top 3 most Serious Defects in Curtain Wall……………………... 112

Fig. 5.3 Compositions of Top 3 Most Serious Defects……………………. 113

viii

List of Tables

PAGE

Table 2.4.1 The Ratings of Defect Quantifying Factors………………………. 62

Table 2.4.2 Results of Defect Ratings ………………………………………... 62

Table 2.5.1 Index and Ranks of Design Defects………………………………. 68

Table 2.5.2 Limitations and Improvements of various Generations of Curtain

Wall System……………………………………………………….

70

Table 2.5.3 Index and Rank of Construction Defects…………………………. 74

Table 2.5.4 Detail List of Factors Affecting Maintenance Practice,

Maintenance Competency and Contractor Competency…………..

79

Table 3.1 Relevant Situations for Different Research Methods…………….. 88

Table 4.1 Possible Defect Items in the Survey Questionnaire………………. 100

Table 5.1 Mean Number / Score of Defects…………………………………. 108

Table 5.2 Rankings of Defects’ Mean Number / Score……………………… 110

Table 5.3 Overall Rankings of Defect Seriousness…...................................... 111

ix

Table 6.1 Possible Defect Causes listed in the Case Study Questionnaire…... 123

Table 7.1 Curtain Wall Design & General Situation of Curtain Wall Defects

of Building no.1…………………………………………………….

130


of Building no.2…………………………………………………….

133


of Building no.3…………………………………………………….

137


of Building no.4…………………………………………………….

140


of Building no.5…………………………………………………….

144

Table 7.6 Ranking of Factors affecting the Occurrence of Defects/ Effect of

Defects by Respondents of Buildings Studied……………………..

148

Table 7.7 Ranking of Factors affecting the Occurrence of Defects/ Effect of

Defects by Respondents of Companies Interviewed……………….

155

Table 7.8 Defects’ information of Building no. 1 to no. 5…………………... 159

x

Table 7.9 Mean Score in the Ranking of Factors affecting the Occurrence of

Defects/ Effect of Defects…………………………………………

161


Defects/ Effect of Defects…………………………………………

163

Table 8.1 Defect Items received Top Four Ranks in their Incidence………... 166

Table 8.2 Defect Items received Top Four Ranks in their Seriousness……… 167

Table 8.3 Rankings Defects’ Causes by different Buildings / Company……. 170

xi

List of Photos

PAGE

Photo 7.1 Photo showing 1 Side of Curtain Wall being too close to an

Adjacent Building…………………………………………………

139

Photo 7.2 Photo showing only the Outer Face of the Connection is Applied

with Sealants………………………………………………………

142

Photo 7.3 Sealant Failure of the Building no.5……………………………... 146

Photo 7.4 An example Glass Panels being Opened Widely………………… 147

Photo 7.5 Design of Operatable Part (Scuttle) of Curtain Wall in Building

no.4………………………………………………………………..

147

xii

Chapter 1 – Introduction

Chapter 1

Introduction

1.1 Background

In recent years, there has been an increased use of curtain wall systems as the external

walls of office buildings. With advantages of good appearance, space saving, lightness

and rapid construction, curtain wall is very attractive to designers. Indeed, curtain

wall is not a new method of building enclosure for the construction industry.

According to Centre for Window and Cladding Technology (CWCT), the first use of

curtain walling appeared in 1917. It was designed by Willis Polk for the envelope of

the Hallidie building in San Francisco. In addition, the increase in the level of

construction technology let curtain wall be designed in more innovative ways.

Innovative designs like glass wall and skylight are developed from curtain wall

system. However, there are not many books discussing curtain wall system. Even for

design of curtain wall, Zhou (2002) is surprised to see how few books are related to

curtain wall design. Books or journals specifically discussing curtain wall defects are

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even much little.

It should be noted that the consequences of curtain wall defects could be very serious.

An example of serious curtain wall defects was the shattering of curtain walls of

several buildings in Wan Chai by Typhoon York in 1999. According to the Hong Kong

Observatory (2000), smashing of more than 400 glass panels in Revenue Tower,

Immigration Tower and Wan Chai Tower occurred. Some confidential documents

were discovered to be blown away by the typhoon. Fortunately, no one was hurt by

this curtain wall defects. Straight after the typhoon, Buildings Department (2003)

issued a practice note concerning curtain wall systems. In the practice note, Buildings

Department (2003) suggests that

“If not properly designed, constructed and maintained, danger to occupants of

buildings and the public could be caused particularly during typhoons. It is therefore

necessary for Authorized Persons (APs), Registered Structural Engineers (RSEs),

building owners and the Building Authority to take great care in dealing with curtain

walls in the interest of public safety.”

In view of these, this dissertation undertakes an empirical investigation on the defects

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in curtain wall, together with their causes behind.

1.2 Aim

The primary aim of this study is to investigate the causes of defects of curtain wall

systems in high-rise office buildings.

1.3 Objectives

1. To find out major forms of curtain wall defects in Hong Kong high-rise office

buildings.

2. To assess the seriousness of curtain wall defects in Hong Kong high-rise office

buildings.

3. To determine the major causes of curtain wall defects and their effects on Hong

Kong high-rise office buildings

1.4 Hypothesis

The curtain wall defects in Hong Kong high-rise office buildings are caused by design

faults.

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1.5 Methodology

To fulfill the objectives, this research is firstly divided into two major parts. The first

part is to examine major forms and seriousness of the curtain wall defects. The second

part is to examine the causes of curtain wall defects. For each of the two parts, the

methodology is carried out in two ways. The first way of them is in common. It is by

reviewing the literatures. However, the second way in each part is different.

In the first part, in order to collect data for major forms and seriousness of curtain

wall defects, a survey is conducted in local high-rise office buildings. The possible

forms of curtain wall defects listed in the Survey Questionnaire are found in

reviewing various literatures. The “defect quantifying factors” used by Chew and

Silva (2004) are used as an instrument to assess the seriousness of defects.

Case studies are conducted in the second part to collect empirical data for determining

causes of curtain wall defects, as well as to find out the effects of such causes on

curtain wall defects. In the case studies, Building Managers / Maintenance Officers

are interviewed in person and asked to fill in a questionnaire. Similar to that of the

Survey Questionnaire, the possible causes of curtain defects listed in the Case Study

Questionnaire are found in reviewing various literatures. The detail methodology is

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discussed in Chapter 3.

1.6 Organization

The study is divided into eight chapters in order to fulfill the objectives. Below are

their titles and the introductions of contents.

Chapter One – Introduction

Chapter One is the introduction of the study. The background, aim, objectives,

hypothesis and methodology of the study are discussed in the chapter.

Chapter Two – Literature Review

Chapter Two is mainly divided into three parts. The first part is to provide overviews

of various types of curtain wall system which are related to curtain wall defects. As

different choices of types and components of curtain wall may affect the chance of

curtain wall defects’ occurrences, they are discussed in the chapter’s first part. With

the same reason, three activities involved in the life of a curtain wall – design,

installation and maintenance are also discussed.

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For the second part, it is a review of literatures related to types and possible causes of

curtain wall defects. It aims at summarizing different types and possible causes of

curtain wall defects mentioned in various literatures. After identifying the possible

causes, a critical review of different arguments on “why curtain wall defects occur” is

addressed in the latter part of the chapter.

Chapter Three – Research Design

Chapter Three illustrates the rationale of the research design. The grounds behind

each research methods used are also explained. Moreover, reasons why particular data

collection and analysis methods are used are discussed in the chapter.

Chapter Four – Survey Questionnaire

In Chapter Four, how the Survey Questionnaire is constructed is shown. The possible

defects identified in the literature review are listed also. This is done to help the

achievement of Objective 1 and Objective 2. The method of determining defects’

seriousness is discussed in the latter part of the chapter.

Chapter Five – Discussion of Survey Questionnaire Results

Chapter Five shows the results and findings of the questionnaire. The description of

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respondents is firstly given. To decide the seriousness of defects, analyses of the

results are presented in the chapter. The analysis is done by calculating the mean

scores of the defects’ incidences, as well as the levels of various factors affecting

seriousness indicated by the respondents. The implications of the results are also

discussed. These help to fulfill Objective 1 and Objective 2.

Chapter Six – Case Study Questionnaire

Similar to Chapter four, how the Case Study Questionnaire is constructed is shown.

The possible defects’ causes identified in the literature review are listed also. This is

done to help the achievement of Objective 3. The method of rating defects’ causes is

discussed in the latter part of the chapter.

Chapter Seven – Case Study Findings Analysis and Discussion

The first part of the chapter is similar to that in Chapter Five. Quantitative analyses of

data from each building or company are separately held. Evaluation of the relative

effect of defects’ causes is done by averaging the indicated levels of importance by

the respondents. In the second part of the chapter, a qualitative study of information

collected from each building or company are separately held. Defects’ causes and

their effects on curtain wall are addressed. Straightly after the qualitative study, a

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general discussion of the combined result is presented. These fulfill the Objective 3.

Chapter Eight – Conclusion

Being the last chapter in the study, Chapter Eight is an evaluation of results and

findings in previous chapters. Whether the results and findings fulfill the three

objectives in the study is discussed. In addition, limitations and recommendations of

further investigation are illustrated in the chapter.

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Chapter 2 – Literature Review

Chapter 2

Literature Review

2.1 Introduction

This chapter aims at reviewing literatures relating to curtain wall, curtain wall defects as

well as their causes. Definition of important terms used in this dissertation is firstly stated.

After the important terms defined, the chapter is mainly divided into three parts. The first

part is to provide overviews of various types of curtain wall system which may be related

to curtain wall defects. As different choices of types and components of curtain wall may

affect the chance of curtain wall defects’ occurrences, they are discussed in the chapter’s

first part. With the same reason, three activities involved in the life of a curtain wall –

design, installation and maintenance are also discussed.

For the second part, it is a review of literatures related to types and possible causes of

curtain wall defects. It aims at summarizing different types and possible causes of curtain

wall defects mentioned in various literatures. After identifying the possible causes, a

critical review of different arguments on “why curtain wall defects occur” is addressed in

the latter part of this chapter.

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2.2 Definition of Terms

Because the defects of curtain wall in Hong Kong high-rise office buildings are examined

in this dissertation, there are altogether 3 terms need to be defined before the discussion.

They are the terms “curtain wall”, “defect (of curtain wall)” and “high-rise office

building”.

2.2.1 Definition of “Curtain Wall”

By the Centre for Window and Cladding Technology (CWCT, 2000), curtain wall is

defined as

“a form of vertical building enclosure which supports no load other than its own weight

that of ancillary components and the environmental forces which act upon it.”

This definition clearly states that the curtain wall is a system which is structurally

independent to the building structure. However, it may not give one a very clear picture

of what is curtain wall.

In Standard Method of Measurement for Building Elements published by the

Architectural Services Department (2001), the components of curtain wall are

stated as

“glass, paneling, louvers, trimmings, fixings, doors, ironmongery, decoration and other

associated works”.

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This shows to the builders that other than glass and aluminum, panels and louvers can

exist in a curtain wall system. Indeed, Brookes (1939), defines curtain wall in a similar

way. Other than what CWCT stated, it further describes curtain wall

“usually consists of a rectangular grid of vertical or horizontal framing with infill panels

of glass or some other lightweight panel”.

With the above three statements, the curtain wall is defined as a form of vertical building

enclosure which supports no load other than its own weight that of ancillary components

and the environmental forces which act upon it. Moreover, it usually consists of a

rectangular grid of vertical or horizontal framing with infill panels of glass or some other

lightweight panels.

2.2.2 Definition of “Defect (of Curtain Wall)”

According to the Oxford Dictionary of English (2nd edition revised), “defect” means

“The fact of being wanting or falling short; lack or absence of something essential to

completeness (opposed to excess); deficiency.”

Therefore, in this study, the author regards curtain wall having “defect(s)” when

incompleteness appeared on the curtain wall. In other words, if a curtain wall system fails

to satisfy one or more of its requirements, the curtain wall is defined as having defects.

These defects maybe the failures or damages of particular parts of the curtain wall system.

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In order to set a boundary for such incompleteness of curtain wall, the requirements of

curtain wall are discussed. As curtain wall is a type of building’s exterior wall, the

principal requirements of an exterior wall listed out by Hutcheon (1963) are studied. They

include requirements listed as follows.

- Control heat flow

- Control air flow

- Control water vapour flow

- Control rain penetration

- Control light, solar and other radiation

- Control noise

- Control fire

- Provide strength and rigidity

- Be durable

- Be aesthetically pleasing

- Be economical

Therefore, if a curtain wall system fails to satisfy one or more of the above requirements,

it could be defined as having “defect(s)”.

2.2.3 Definition of “High-rise Office Building”

The definition of “office building” is given by the technical notes of Rating and Valuation

Department. The definition is as follows;

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“Private Office premises comprise premises situated in buildings designed for

commercial/ business purposes.”

For the definition of “high-rise building”, it varies in different countries as well as in

different periods of time. Therefore, in this dissertation, it is defined as buildings having

more than or equal to 20 storeys.

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2.3 About Curtain Wall

2.3.1 Structure of Curtain Wall System

2.3.1.1 Types of Curtain Wall

The classification of types of curtain wall varies in different countries or even trades.

However, the CWCT (2000) tries to classify types of curtain wall as follows;

- Stick

- Unitized

- Panelized

- Spandrel panel ribbon glazing

- Structural sealant glazing

- Structural glazing

The differences between the above types of curtain wall are mainly their means of support,

means of assembling and their appearances. On the other hand, Chew (2001) identifies

different kind types of curtain wall with the review of the curtain walls’ development

history. Three generations of them are identified.

The first generation is from year 1800-1960. In this period, curtain wall is designed based

on the fixing of vertical mullions to which horizontal rails or transoms. Frames and

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insulated panels are attached on them. This system is called stick system. Its typical

structure is as shown in Fig. 2.3.1.

Fig. 2.3.1 A Typical “Stick System”

Source: Chew (2001)

The second generation mentioned by Chew (2001) is the period of year 1960-1980. In

this period, a system called panel (or unitized) system is used. The whole system is

composed of panels or units of usually one floor high and one bay wide. Each of them is

composed of at least one female mullion on one side, one male mullion on the other side

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(Zhou, 2002). Together with the stick system developed in the first generation, these two

kinds of curtain wall system are called “basic forms of curtain wall construction”

(Brookes, 1998). Typical structure of the panel system is as shown in Fig. 2.3.2.

Fig. 2.3.2 A Typical “Panel System”

Source: Chew (2001)

The third generation is year 1980 onwards. This generation is mainly characterized by its

techniques improvement. Structural sealants and adhesives are used widely. The uses of

curtain wall are much diversified in its third generation. Special and innovative types of

curtain wall (e.g. structural glazing and suspended glass assemblies) appeared.

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Toughened glass, vertical glass (or metal) fins, and specially designed clamp-like fittings

are the mainly used in these types of curtain wall.

2.3.1.2 Components of Curtain Wall

In this section, the components of basic forms of curtain wall will first be identified, and

then a common connection system between them is to be discussed. According to the

above definition of curtain wall, a curtain wall system is composed of;

- Glass

- Paneling

- Louvers

- Trimmings

- Fixings

- Doors

- Ironmongery

- Decoration and

- other associated works

From the above list, it is noticed that the main components of curtain wall are glass,

paneling and fixings. The joint design which is always an important part of curtain wall

should also be one of them.

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2.3.1.3 Properties of Main Components of Curtain Wall

1) Glass

It is used in building facade mainly because of its transparency, light and reflective.

However, glass is a material which failure under any type of load is brittle and without

prior signs for distress (Dalgliesh, 1998). Therefore, the limitations of each type of glass

should be noticed.

For the construction of curtain wall in Hong Kong, there are mainly three types of glasses,

namely float glass, heat strengthened glass and tempered glass (Zhou, 2002). Josey (1997)

writes a paper describing the properties these types of glass. The paper is summarized as

follows;

Float glass

Float glass is also called ordinary annealed glass. In thin sheet form, this type of

glass is not a safety material. It is because when there is a sudden impact of huge

load, float glass breaks into sharp-edged, pointed pieces. Some of these pieces can

be large and potentially lethal, and all of which can cause injury. Therefore, it can

be considered as a safety glass only when it is sufficiently thick to resist breakage.

Heat Strengthened Glass

Heat Strengthened Glass is formed by float glass heated to 550oc and cooled down

quickly. The bending strength of this type of glass is double of that of float glass.

Although the strength is doubled, the pattern of breakage remains the same.

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Because of this, heat strengthen glass is also not considered as a safety glass

unless it is thick enough.

Tempered Glass

Tempered Glass is also called toughened glass. It is formed also by heating the

float glass, but in a higher temperature (650 oc) and cooled in a more rapid way

than that of heat strengthened glass. For this type of glass, the compressive stress

at the surface is balanced by tensile stress in the interior. Therefore, tempered

glass has higher allowable stress (Zhou, 2002). With the same thickness of glass,

tempered glass can resist higher wind loads. Another advantage of tempered glass

is that it can resist much higher temperature (250-230 oC) compared with float

glass (70-100 oC) (Zhou, 2002). As the forces are balanced in the glass, this type

of glass cannot be worked or cut after toughening. Unlike float glass and heat

strengthened glass, when tempered glass breaks, they remain within the frame. It

is because when it breaks, there is a release of energy from the glass. Therefore,

expansion occurs and broken pieces of glass are locked in place. Another

characteristic of tempered glass is that upon breakage, tempered glass smashes

into small pieces of non-pointed glass beads. With these two reasons, tempered

glass is regarded as a safety glass.

Details of performance characterizes of glass is listed by Wong (1998) in a table, which is

attached in Appendix A.

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2) Paneling

In the curtain wall systems, type of paneling commonly used is rolled aluminum sheet

panel. It is panel consists of 3-6 mm sheet aluminum formed into a tray, or by spot

welding angles that form the edge to the tray. The stiffness of the panel depends on the

thickness of the aluminum and the number of stiffening angles. As the thermal expansion

of this type of cladding is quite great, the design of expansion joints is one of the main

considerations (Brookes, 1998).

Details of performance characterizes of aluminum is listed by Wong (1998) in a table,

which is attached in Appendix A.

3) Fixing

The material used for fixing in curtain wall system (e.g. embedment, transom and mullion)

is usually aluminum alloy. Although aluminum naturally forms a continuous and strong

oxide film that prevents further corrosion, anodizing is required for high quality

requirements of materials used in curtain wall construction. Anodizing can increase the

thickness of the protective layer artificially. Another issue should be noted is welding of

aluminum alloy. According to Zhou (2002), most aluminum can be welded. He also

pointed out that for the tempered aluminum alloy, welding may reduce the strength of the

alloy as the tempering will be lost during the heating process of welding.

4) Joint Design

According to Chew (2001), there are three methods to seal the joints. They are filled joint,

gasket joint and drained joint. They are designed for claddings system like metal cladding

system and curtain wall system.

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Fig. 2.3.3 Details of Single-stage Joints: a (i) Filled Joint and (ii) Gasket joint

Source: Chew (2001)

Filled Joint

Filled joint (see. Fig. 2.3.3) is classified as single-stage joint which its joint

material functions both as a rain and air barrier. To achieve this, sealants are used

in filled the joint. Completely sealing off the joint by sealants is required (Chew,

2001).

According to Zhou (2002), sealants are classified in two types on their uses. The

first of them is weather sealant. Weather sealant usually has a low elastic module,

low hardness, less strength. It also allows more movement and only used to seal

joints for water or air-tightness. The other type is called structural sealant. This

type of sealant has higher elastic modulus, higher hardness, higher bonding

- 21 -


strength, higher strength in resisting tensile and compressive and shear stress.

Structural sealant is usually used in filled joints structural glazing where glasses

are directly adhered together.

Gasket Joint

Like filled joint, gasket joint (see. Fig. 2.3.3) is also classified as single-stage joint.

It uses gaskets which are tailor-made plastic fittings to fit into the gap of panels.

Unlike sealants, gaskets are not adhesive. They only rely on pressure compressing

each other to provide a weather seal. Therefore, they should be made from

materials which are compressible, impermeable to moisture, with high resistance

to environmental agents, and high elastic recovery. The dimensional accuracy of

the gaskets during manufacture is very important. Pressure in-service is required

to ensure effectiveness. Although gaskets make the installation more accurate and

simple, slight deformation of panel can result in complete failure of the joint

(Chew, 2001).

Fig. 2.3.4 Details of a Drained Joint

Source: Chew (2001)

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Drained Joint

Drained joint (see Fig. 2.3.4) is classified as multiple-stage joint where rain barrier

and air barrier are separated. It appears in second generation of the curtain wall

system. It uses neoprene baffle to divide the spaces of joint into two sections. The

out section firstly drains away most of the water which enters. For the inner

section, there is an air chamber which provides a second line of defence to any

water by-passing the first section. In the air chamber, because of the incorporation

of a wind (or air) barrier, the wind pressure difference across a cladding is reduced.

Reducing of wind pressure differential will decrease the chance of water

penetration into the panel. It is because such pressure differential is the primary

mechanism to cause water penetration by providing force required to drive water

into the panel. Fig. 2.3.5 shows an example of such pressure equalization system

preventing water penetration (Chew, 2001).

In addition to better water penetration prevention, the protection of air barrier in

the joint is another advantage of the drained joint. In a drained joint, air barrier is

not located on the outer surface of the curtain wall (Chew, 2001). This ensures the

air barrier is shielded from the effects of sunlight. Another advantage of a drained

joint mentioned by Chew (2001) is that a close dependence on tolerance limits is

not required. The risk of loss of adhesion of the jointing material is less critical to

the performance of the joint.

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Fig. 2.3.5 A Pressure Equalization System

Source: Chew (2001)

2.3.1.4 Elements of Connection of Main Components

In connection of the main components, it involves four main elements, namely the main

support structure, the intermediate support fixing, the mechanical fixing and the panel.

Below are brief descriptions of them (Dowdle and Cole, 1999);

1) Main Support Structure

It is the part of building structure where the curtain wall fixed on. It transfers design loads

from the curtain wall back to the building structure.

2) Intermediate Supports

They provide points of attachments for mechanical fixing and transfers loads to the

support structure. A common method is that brackets are used to fix the mechanical fixing

- 24 -


onto embedment fixed inside the support structure. Examples of such embedment are

Halfen Channels (see Fig. 2.3.6a and Fig. 2.3.6b) and steel plates welded with anchors

(see Fig. 2.3.7a and Fig. 2.3.7b) (Zhou, 2002). For the intermediate support fixing, in

order to let the system allow various movements (e.g. thermal movement and settlement),

tolerance is installed. It is done by using oversized and slotted holes, instead of well-fitted

holes in connecting the components.

Fig. 2.3.6a A Fixing System using Brackets and Halfen Channels

Source: Zhou (2002)

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Fig. 2.3.6b An Isometric view of Fixing System using Brackets and Halfen Channels

Source: Zhou (2002)

Fig. 2.3.7a A Fixing System for the Stick System using Brackets and Steel Plates welded

with Anchors

Source: Zhou (2002)

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(i) (ii)

Fig. 2.3.7b A Fixing System for the Unitized System using Brackets and Steel Plates

welded with Anchors (i) View form Above and (ii) Lateral View

Source: Zhou (2002)

3) Mechanical Fixings

They support the glass and transfer the glass self-weight and lateral loads to the

intermediate support. For stick and unitized curtain wall system, they are mullion and

transom. For the connection of intermediate supports and mechanical fixings, bolts and

nut are usually used. The connections of mullion and transom are usually by bolting

aluminum angles (see Fig. 2.3.8), using tenon (see Fig. 2.3.9) or bolting directly by

screws (see Fig. 2.3.10) (Zhou, 2002).

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(i) (ii)

Fig. 2.3.8 (i) Aluminum Angles are used for Connecting Mullion and Transom (ii) An

Isometric View of an Aluminum Angle

Source: Zhou (2002)

Fig. 2.3.9 A Tenon Joint used for Connecting Mullion and Transom

Source: Zhou (2002)

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Fig. 2.3.10 Screws Directly Applied from Mullion Side into Transom’s Screw Holes

Source: Zhou (2002)

4) Panel

Structurally, it transfers loads to mechanical fixing. For glass panels, the connections of

the glazing and the mechanical fixings are usually by aluminum glazing beads (see Fig.

2.3.11a and Fig. 2.3.11b) or adaptors (see Fig. 2.3.12). For aluminum glazing beads, there

are two types, namely triangular beads and square beads. Different from glazing beads,

adaptors were glazed to the glass panel in factories and shipped to site. On the site, the

adaptor is fixed to mullion or transoms with clamping bars and screws. Therefore,

compared to glazing beads, adaptors give a better quality of sealant application (Zhou,

2002). For light weight metal panels, aluminum clamping plates (see Fig. 2.3.13a) are

commonly used to fix the panels (see Fig. 2.3.13b). These plates are located within the

UPVC edge profiles (see Fig. 2.3.13c) and behind the primary gaskets.

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Fig. 2.3.11a Triangular Beads used to Fix Glass Panels

Source: Zhou (2002)

Fig. 2.3.11b Square Beads used to Fix Glass Panels Source: Zhou (2002)

- 30 -


Fig. 2.3.12 Adaptors, Clamping Bars and screws used to Fix Glass Panels Source: Zhou (2002)

- 31 -


Fig. 2.3.13a Aluminum Clamping used to Fix Metal Panels

Source: Brookes (1998)

Metal Panels

Aluminum clamping

UPVC edge profiles

Metal mullion

Fig. 2.3.13b Details of Connection between Panels, aluminum Clamping and Metal

Mullion


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Fig. 2.3.13c Installation of UPVC Edge Profiles


- 33 -


2.3.2 Design of Curtain Wall System

2.3.2.1 Design Requirements

As mentioned in Chapter 2.2, the design requirements of curtain wall are listed out by

Hutcheon (1963).These requirements can be grouped into three areas, namely the

performance requirements, the structural requirements and durability requirements.

1) Performance Requirements

They are the capability of the curtain wall to control heat flow, air flow, water vapour

flow, rain penetration, radiations, noise and fire. Satisfying these requirements means the

buildings can provide its occupants an indoor environment which is good and safe.

2) Structural Requirements

It requires the curtain wall to provide strength and rigidity. To ensure the structure have

adequate strength to hold itself after being install onto the building structure, designers

should consider the dead loads and live loads of the structure. The dead load is defined as

‘intrinsic weight of a structure or vehicle, excluding the weight of passengers or goods’,

while live load is defined as ‘the weight of people or goods in a building or vehicle’1. For

curtain wall, as it is defined as non-structural load bearing for the building, the dead load

is the weight of its components. The live loads are the occasionally imposed static and

dynamic loads. Examples are wind load, thermal stress and weight of rain water carried

through the drained joints’ drainage zone.

1 The Oxford Dictionary of English (2nd edition revised)

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Most of the live loads of curtain wall are from natural environment. Therefore, the system

should be designed capable to withstand impacts from the natural environment. To

achieve this, wind loads should be calculated to resist the great force acting on the curtain

wall by strong winds and gusts. Gusts, which are relative small-scale (and hence high

frequency) of winds, are claimed by Eaton (1978) to be one of the major causes of curtain

wall damage. It is because gusts vary the change nature of wind force rapidly from

pressure to suction and vice versa. To prevent structures from being damaged by wind,

many scientists such as Kumar (1999) try to predict the wind-induce fatigue on the

claddings. He does this by simulated the wind loading pattern and inputting local climate

data as well as amplitude tests result data. In addition to wind damage on the whole

system, wind damages on individual components of curtain wall system have also been

analyzed by the scientists. One example is the mathematical model developed by

Vallabhan, Asik and Kandil (1995) for analyzing the sealant of curtain wall system.

Vallabhan et al (2005) ’s mathematical model calculates the required strength for the

sealant to resist different strengths of lateral pressure. It is done by idealizing the sealant

as three springs located in three different planes. These predictions and mathematical

models also are very important in designing curtain wall systems.

However, mentioned in the Explanatory Materials to the Code of Practice on Wind

Effects in Hong Kong 2004, although the wind characteristics for Hong Kong

environment had been discussed by many researchers in the past (Mackey, 1970; Ko,

1972; Chen, 1975; Choi, 1984; Davenport, Georgiou, Mikitiuk, Surry and Lythe, 1984;

Melbourne, 1984; Jeary, 1994; Holmes, Hitchcock, Kwok and Chim, 2001), the wind

characteristics near the ground in Hong Kong associated with building design are still not

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fully understood. The explanatory materials explain this by pointing out there are

difficulties involved in both the understanding of typhoon structure over large hills or

mountain, as well as the measurement of wind characteristics during typhoons. These

makes predictions of required strength for curtain wall (also for its individual components)

are difficult for designers.

Major effects of factors affecting the structural performance are also discussed by Chew

(2001). Chew (2001) identified three types of factors affecting the structural performance.

These three types of factors cause curtain wall components’ differential movements to

occur in various axes. They are wind (causing components to move in x-axes), weight

(causing components to move in z-axes) and thermal/ moisture (causing components to

move in y-axes). Their effects on curtain wall system are illustrated in Fig. 2.3.14. All of

them should also be considered by designers.

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Fig. 2.3.14 Movements due to Moisture, Temperature, Creep and Differential Settlement

Source: Chew (2001)

3) Durability Requirements

Other than being capable to withstand impacts from the natural environment, the system

should be durable in order to keep the maintenance cost a minimum. To ensure the

durability of curtain wall, Mayer and Brewer (2001) propose a method for auditing the

durability. One of the aspects considered will be the design. The design section of the

suggested audit is concentrated on a limited number of key items. They are weather

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protection, interfaces between dissimilar materials, the conjunction between curtain wall

and the structure, and the wind load likely to be faced.

To study the durability for curtain wall, Chew, Tan and Soemara (2004) hold a survey to

examine the behaviour of materials used in facades (including glass and aluminum) and

wet areas in tropical climates. They find that compared with those in urban and suburban

areas, the durability of all examined façade materials locating in industrial zone and near

expressway are the lowest. This shows that high level of pollution increases the

deterioration rate of the curtain wall system. Therefore, it is important for curtain wall

designers to consider the proposed building’s environment in the design stage. The

identified environmental attacks that cause external walls to gradually degrade include

extremes of temperature, solar radiation, ultraviolet light, acid rainfall and other

atmospheric pollutants. They should be considered by designers in the design stage

(Willmott and Harris, 2001). According to Willmott and Harris (2001), some of the

elements used in the systems (e.g. coating of the claddings) have been extensively tested

for their resistance atmospheric agents.

However, it is not always easy for designers to know exactly what the environment will

be. It is because not only the environment varies throughout places, the local and global

climates have varied throughout the time. Yates (1998) raised a concern in the CIB World

Building Congress about these changing climates may effect the durability of building

components. Thus the designer should study the environment of the location of the

proposed building, as well as the climates around that area and account them in the

curtain wall design.

- 38 -


As the determination of claddings occurred over time, other than their durability, when

they should be replaced is a matter concerned. Shohet and Paciuk (2004) manage to

predict the service life of various claddings such as mortar and stone claddings by

developing typical deterioration paths developed from field survey data. They also

conclude that the deterioration of claddings examined can be characterized by linear

patterns.

2.3.2.2 Regulations and Standards

1) Statuary requirements

According to Building (Construction) Regulation 43(1), (2), (3) and (5),

“(1) Every curtain wall shall safely sustain and transmit to the load-bearing structure

the combined dead loads, imposed loads and wind loads without such deflection or

deformation as will cause the curtain wall damage or impair its stability.

(2) Every curtain wall shall-

(a) be constructed entirely of non-combustible materials; and

(b) be designed in accordance with recognized engineering principles relating to

the design and structural use of materials for curtain wall construction.

(3) The connection of curtain wall supports to the load-bearing structure shall not in

any way impair the structural integrity or behaviour of the member to which the

support is being fixed and the supports shall be fixed to the structure by-

(a) a cast-in anchorage in a structural concrete member; or

(b) being welded to a structural steel member.

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(5) Where materials or a combination of materials used in the construction of a curtain

wall may be affected by electrolytic or chemical action the surface of such

materials shall be satisfactorily treated or separated to prevent corrosion.”

The above described curtain wall should being designed for satisfying its structural and

performance requirements. However, this regulation is quite descriptive. A more practical

one is stated by Buildings Department (1999),

“Authorized Persons and Registered Structural Engineers should include the following

in the curtain wall plans for submission to the Building Authority for approval :

(a) structural details and calculations and the installation procedures;

(b) evidence of electrolytic action and corrosion prevention;

(c) elevations including panel arrangements;

(d) typical and non-typical sections showing structural members and supports;

(e) typical and non-typical connections;

(f) specifications on allowable tolerance of the positioning of curtain wall supports

and any remedial arrangements in cases where such tolerance is exceeded;

(g) the mode of support from and connection to the load-bearing structure of the

building (anchorages in structural concrete members or welded connections to

structural steel members) and any justification and application for modification

of the Building (Construction) Regulation 43 for using other mode of support,

eg, drilled or bolted fixings;

(h) quantitative provision for lighting, ventilation and minimum requirement of

prescribed windows (Building (Planning) Regulations 30 and 31 refer); and

(i) standard specifications or codes of practice on structural glazing.”

- 40 -


The above shows that the government concerns the details, calculation, installation

procedure, the durability of materials, panels arrangements, support, connections,

installation tolerance and performances of curtain wall. The structural glazing, which is a

new type of curtain wall system which is not yet widely used for office buildings in Hong

Kong, is specially noticed by the authorities.

In addition, according to the Buildings Department (2003), as curtain wall is a type of

cladding systems, it should be provided with sufficient permanently flexible joints

horizontally and vertically to cater for the differential movement in the cladding and in

the structure to which it is attached.

2) International Standards of Components

In Hong Kong, there is no specific standard is specially required by the authorities for the

curtain wall. Instead, the Building Department accepts national standards and code of

practice that commonly used and accepted in Hong Kong. According to Zhou (2003) and

Buildings Departments (1999), the national standards of the components listed are as

follows (note that sealants have no international standards);

Panels and Fixings - Aluminum Alloys

Aspect National Standard

Property of Aluminum Alloys BS2 8118

Material (chemical) compositions of alloys BS 1470 to 1474

2 BS = British Standard

- 41 -


Coating thickness and materials BS 3987

Protection of anodized surface BS 3987, PD 6484

Structural calculation BS 8118

Glazing - Glass

Aspect National Standard

Property of Glass BS 6262

Material (chemical) compositions of glass BS 952: Part 1

Tolerance BS 952: Part 1

Works on glass BS 952: Part 2

Calculation of glass thickness and type required BS 6262

Safety performance specifications & test method ANSI3 Z97.1

Standard specifications: heat-treated flat glass ASTM4 C1048

Standard specifications: basic soda lime silicate glass BS EN5 572

3) Wind Code

To ensure the structure can stand in the strong winds, Buildings Department requires the

superstructure as well as foundation in building development proposals to satisfy the

Code of Practice on Wind Effects in Hong Kong. For decades, the wind code published in

1983 had been used by designers in determining the design wind pressure on the

buildings.

3 ANSI = American National Standard Institute 4 ASTM = American Society for Testing and Materials 5 BS EN = British and European Community Standard

- 42 -


Until recently, the code has been renewed. It will be enforced starting from December

2004 with a one-year transition period. In the new version of code, for the external

building elements (e.g. curtain wall), the method of calculation for the total wind force

acting on the building is the same. On the other hand, the wind channel down effect is

accounted in the figures used in the calculation. It states that the design wind pressure

shall be a constant value over the lower part of the building. The height up to which this

constant value occurs is to be taken as the breadth of the building or the actual height of

the building, whichever is the lesser. This constant value shall be taken as the design wind

pressure at this height, instead of using values which vary with the building height

(Buildings Department, 2004).

The equation used to find the total wind force Fp acting in a direction normal to the

individual elements as follows (Buildings Department, 2004);

Fp = Cp qz Am

where Cp is the total pressure coefficient for individual elements6

qz is the design wind pressure corresponding to the height z of the element7; and

Am is the surface area of the element.

4) Safety Tests

Straight after the design of curtain wall being finished, tests are required. These tests are

done for ensuring the design actually can withstand impacts from the environment. In the

Building (Construction) Regulations 43 (6), it requires ‘the suitability and adequacy of

every curtain wall shall be demonstrated by tests.’ 6 for curtain wall, it is -1.4 or +1.0 in edged zone and -1.0 or +1.0 in other surface of building 7 determined in accordance with section 4 of Code of Practice on Wind Effects in Hong Kong – Attached in Appendix B

- 43 -


According to the Buildings Department (1990),

‘curtain wall systems without a history of previously accepted test will be required to

undergo a safety test to confirm that they will perform satisfactorily. The test shall be

carried out on a specimen of at least one floor height and shall include the different

features of the curtain wall being used. The test may either be a cyclic test or static load

test.’

Cyclic test and static load test are held in laboratory according to BS 5368: Part 3. They

are used for examining the curtain wall’s serviceability and safety after withstanding the

positive and negative wind pressures. The design passes the test if it is capable of the test

pressures without damage or losing serviceability, and that any residual deformations are

within prescribed limits (CWCT, 1996). Other than cyclic and static load tests that

examine the structural safety, CWCT (1996) issued a series of guidelines for testing for

air leakage, water penetration, water-tightness, thermal expansion of components, and the

curtain wall’s ultimate strength.

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2.3.3 Installation of Curtain Wall System

2.3.3.1 Installation Procedures

Different design and types of curtain wall involve different installation procedures. Chew

(2001) lists out the procedures of two common types of curtain wall, namely typical stick

system and typical panel/unitized system. Below are the procedures mentioned by Chew

(2001).

1) Typical Stick System

First, main markings are set out.

Second, anchorage angle plates are cast to the floor

Third, fasteners are fixed. These fasteners are used to cater for movements of the

components. An example of fastener is as shown in Fig. 2.3.15

Fourth, vertical mullions are installed. In joining two pieces of mullions, a “T” piece is

slid into tailor-made rails in the mullions and welded to hold its place (see Fig. 2.3.16).

Fifth, horizontal transoms are installed.

Sixth, glass and metal panels are installed.

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Seventh, fire stops and insulations are installed. Fire stops are installed into the gaps

between the panel and the slab. Sealing of such gaps can prevent fire and smoke from

spreading from on floor to another.

Eighth, cover plates are installed.

Ninth, gypsum boards or partitions are installed.

Lastly, the whole system is cleaned.

Fig. 2.3.15 An Example of Fastener – Fastener Fixing Mullion to the Concrete Slab

Source: Chew (2001)

- 46 -


Fig. 2.3.16 Welding of “T” Piece to the Mullion

Source: Chew (2001)

2) Typical Panel/Unitized System

First, main markings are set out.

Second, anchors are cast to each floor

Third, panels are directly hoist up and transferred to their respective locations. In

handling the panels, various systems like monorail system, gear and cog pulley system

and manual craned can be used.

Fourth, alignment is checked before installation of panels.

Fifth, the panel is slid into its neighbour to ensure water tightness.

- 47 -


Lastly, the whole system is cleaned after all panels are installed.

2.3.3.2 Installation Requirements

High quality of installation is essential for good performance and high durability of

curtain wall. In view of this, high standard of workmanship should be ensured. However,

specific installation requirements for curtain wall are seldom discussed. Therefore, it is

expected that like other parts of work in the construction, workers should at least follow

the requirements of material used, the method of construction, and the level of

workmanship that is required in the specification. To ensure the qualities of curtain wall

in design, construction and maintenance aspects, as mentioned in the previous Chapter

2.3.2, Mayer and Brewer (2001) propose a method for auditing the durability. In the

workmanship section of the suggested audit, the durability of curtain wall is to be ensured

by auditors visiting the site with a checklist. This checklist is specified for curtain wall

installation. Items include method and location of site storage, the seriousness of site

alternations, the continuities in inter-components’ insulation, and the method use in

isolating incompatible materials are listed in the checklist. Each of the items has to be

checked carefully by the auditors. With such auditing system, the quality of curtain wall

construction could be more ensured.

- 48 -



For different designs of curtain wall, the method of installation varies greatly. Therefore,

there are no specific regulations or standards imposed by the government in the process of

curtain wall installation.

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2.3.4 Maintenance Management of Curtain Wall System

2.3.4.1 Definition and types of maintenance

As all elements of buildings deteriorate over time, there are no maintenance-free

buildings and all of them should be maintained properly throughout their designed period-

of-use. In BS 3811, the word “maintenance” is defined as

“The combination of all technical and administrative actions, including supervision

actions, intended to retain an item in, or restore it to, a state in which it can perform a

required function.”

The reasons for retaining the item in a state in which it can perform its required function

are to sustain the utility and value of the building (Seeley, 1987).

Other than defining what “maintenance” is, BS 3811 also classifies maintenance as

various types. They are planned maintenance, unplanned maintenance, preventative

maintenance, corrective maintenance, emergency maintenance, condition-based

maintenance and scheduled maintenance. Their relationships are identified by Seeley

(1987) as shown in Fig. 2.3.17.

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Maintenance

Planned maintenance Unplanned maintenance

Preventative Corrective maintenance Corrective maintenance(including emergency maintenance) maintenance (including emergency maintenance)

Condition-based maintenance

Scheduled maintenance

Fig. 2.3.17 Types of Maintenance

Source: Seeley (1987)

The three most common types of maintenance methods, namely corrective maintenance,

preventive maintenance and condition-based maintenance are discussed in below. Note

that scheduled maintenance, which is carried out in accordance with an established time

schedule is not common in building maintenance;

1) Corrective maintenance

In corrective maintenance, maintenances will be carried out after fault recognition. This

type of maintenance intends to put an item into a state in which it can perform a required

function (BS 3811: 1993). It is said to be failure-based and take place in ad hoc manner in

response to breakdowns or user request (Horner, Haram and Munns, 1997).

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Horner et al (1997) claims that this type of maintenance can be extremely expensive

because of two reasons. The first one is that the failure of an item can cause a large

amount of consequential damage to other elements in the building. The other reason is

that the failure of an item can make manpower and spare parts planning extremely

difficult as failure of an item can occur at anytime. If the time of defects occurred is

inconvenient to both users and other parties involved in building maintenance, the loss of

users as well as to cost for treating such defects could be very high. However, Horner et

al (1997) state that this kind of maintenance is still important in maintenance strategy.

2) Preventive maintenance

In preventive maintenance, maintenance will be carried out at predetermined intervals, or

according to prescribed criteria. It is intended to reduce the probability of failure or the

degradation of the functioning of an item (BS 3811: 1993).

This method is said to overcome the disadvantages of corrective maintenance, and its four

advantages are discussed by Raymond and Joan (1991). First, they mentioned that as in

this type of maintenance, time for planning and performing maintenance is convenient to

the building’s user. Second, the maintenance costs can be reduced by avoiding the cost of

consequential damages, which are let to be occurred in corrective maintenance. Third,

downtime of an element of the building – or the whole building can be minimized so the

habitability of the building can be increased. Finally, Raymond and Joan (1991) claimed

that the health and safety of the user can be improved by using preventive maintenance.

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However, this type of maintenance has its shortcomings. Horner et al (1997) quote the

argument of El-Haram (1995) that a large number of unnecessary tasks carried out on

elements, as well as extremely large amount of resources being used in spare parts and

labour, may be resulted in using preventive maintenance. In addition, human error during

the execution of the maintenance task may also be resulted. This error could make

elements’ conditions end up worse than before.

3) Condition-based maintenance

Maintenance is carried out according to the need indicated by condition monitoring in this

type of maintenance (BS 3811: 1993). This means if a significant deterioration in a

monitored parameter is detected, maintenance is to be carried out. The actual states of

such parameters are examined by a condition survey, where visual inspections and/or

condition monitoring tools will be used (Horner et al, 1997).

2.3.4.2 Actions Involved in Maintenance

After identifying different kinds of maintenance, the actions involved in maintenance are

studied. In general, maintenance comprises three separate main components. They are

serving, rectification and replacement. Below are important points that stated by Seeley

(1987) regarding such three actions.

Serving is sometimes called “day-to-day” maintenance. It is essentially a cleaning

operation undertaken in regular intervals. Its tasks can be easily identified. When these

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tasks should be held could also be easily planned. Services schedules are usually set up

for this kind of maintenance.

Rectification work usually arises from shortcomings in design, inherent faults in or

unsuitability of components, damage of goods in transit or installation and incorrect

assembly. This kind of work occurs usually in fairly early life of the building. The long-

term maintenance cost of the building will be reduced if this kind of maintenance is done

well. This kind of maintenance is usually initiated by failure of a building element in

performing its functions.

Replacement stems not much from physical breakdown of materials or elements. It is

from deterioration of appearance. Therefore, the length of acceptable life often involves a

subjective judgment of aesthetics of change. In addition, the durability or life of material

is very difficult to measure. Together with the fact that service conditions, as well as

environment (which is complex in nature) causing materials to decay at different rates,

decisions of “when replacements should be held” and “how much material should be

replaced” are difficult jobs.

From the above, it can be known that the decision of which action to do is mainly affected

by the nature and causes of such defects. The difficulties associated with these three types

of actions are also identified.

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2.3.4.3 Management Requirements

The requirements and objectives of maintenance are mentioned in previous literatures is

cited by Horner et al (1997);

“- to ensure that the buildings and their associated services are in a safe condition;

- to ensure that the buildings are fit for use;

- to ensure that the condition of the building meets all statutory requirements;

- to carry out the maintenance work necessary to maintain the value of the physical

assets of the building stock; and

- to carry out the work necessary to maintain the quality of the building.”

On the other hand, Horner et al (1997) argue that in current building maintenance

strategies, maintenance is not carried out according to actual need. Instead, the strategies

are most likely to be budget driven. Therefore, the requirement of maintenance cost kept

at optimum level is very important nowadays.

In response to the growing importance of cost optimization, Horner et al (1997) propose a

new approach in maintenance strategies. They suggest an integration of the three

maintenance strategies should be used. In addition, they argue that in constructing the

maintenance plan, property managers should notice that not all items are significant, can

always be condition monitored or can always being able to be monitored in a cost-

effective way. Horner et al (1997)’s “Building maintenance decision diagram” is attached

in Appendix C

- 55 -



1) Buildings Ordinance (Chapter 123)

In the Buildings Ordinance, not like that of curtain wall design and construction, there is

an absence of specific requirements for owners how to maintain the curtain wall. On the

other hand, in Section 26 of Buildings Ordinance, if any building is classified as

“Dangerous Building” or “Defective Buildings” by the Building Authority either in the

aspect of fire, wind, rain, dilapidation, use, lack of fire escapes or any other aspect, the

building will need to be demolished or repaired under the instruction of Building

Authority. However, the content and quality of management are not discussed by this

ordinance.

2) Buildings Management Ordinance (Chapter 344)

The main objective of the Buildings Management Ordinance is to facilitate the

incorporation of property owners to provide for the management of buildings. It also

states that if the buildings are not managed or not properly managed and put to their users

at risk, the ordinance itself can empower the Secretary for Home Affairs to impose

mandatory management on those buildings. However, similar to that of Buildings

Ordinance, details of maintenance management are not discussed.

3) Practice Note for Authorized Persons and Registered Structural Engineers – Curtain

Wall Systems

Buildings Department (1999) issued a practice note about curtain wall maintenance. It

suggests all owners of buildings with curtain wall should make arrangements for the

curtain wall to be inspected regularly, at least twice a year and before and after typhoons.

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The practice note also proposes APs, RSEs and building management personnel to watch

out for signs of distress or deterioration in the inspections. Examples of these signs are

also given.

4) Building Maintenance Guide Book

The Building Maintenance Guide Book was published by the Buildings Department in

2002. Indeed, it is not a statuary requirement. It aims to provide building owners with

essential information on building maintenance matters covering such diversified areas as

statutory requirements, construction technology, project supervision and estate

management. In the book, guidelines on the maintenance are provided. They are listed as

follows;

- whole system should be regularly inspected;

- expansion/ movement joints and sealants should be examined;

- cracked or bulging panels should be removed immediately

- the cause of the defect should be identified and eliminated to avoid recurrence of the

same defect

- if the existing system be identified to be not suitable for the building, it must be

totally replaced

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2.4 Types and Seriousness of Curtain Wall defects

2.4.1 Types of Defects

In the studies and discussion of curtain wall (Chew and Silva, 2004; Tee, 2004; Buildings

Department, 2002; Buildings Department, 1999; Chew, Wong and Kang, 1998), various

curtain wall defects have been discovered. They are listed below in according to the

components being affected;

1) Glass panels:

- cracking / shattering, loosening or falling off

- staining / decolouration

- surface etching

2) Aluminum panels:

- cracking, rotation, displacement, loosening or falling off;

- staining / decolouration;

- bulging with hollow base, bowing,

- separation, delaminating; and

- erosion due to rain water, surface abrasion

3) Fixings (e.g. embedment, mullions, transoms, beads):

- looseness;

- missing parts;

- corrosion; and

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- mechanically damaged

4) Sealants / Joints

(failures mentioned in first two points are visualized in diagrams in Fig. 2.4.1)

- between joints and panels (Chew, et al, 1998):

o adhesion failure – loss of bond between sealant and substrate;

o cohesion failure – failure within sealant material;

o spalling – occur when cohesive strength of sealant is greater than that of

surface layer of material to which it is applied;

o extrusion – ejection from part of the sealant which becomes vulnerable to

mechanical damage and impairs the ability of sealant

remaining in the join to perform its function;

o intrusion – occurs when sealants surface is penetrated by grit and debris;

o waisting – resulting from viscous flow which finally leads to thinning of

the sealant in part of the joint;

o slumping – sealants flows downwards as a result of gravity / soften

sealants;

- hardening/weathering/crazing (caused by loss of solvent or plasticizers, ultra-violet

radiation or ozone);

- softening (caused by improper curing or thermal/ photochemical degradation of the

polymer);

- split; and

- missing

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Fig. 2.4.1 Types of Sealant Failure

Source: Chew, Wong and Kang (1998)

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5) Others (affecting performance requirements):

- water seepage

- excessive air permeability / vacuum layer failure; and

- moisture behind curtain wall (between the 2 pieces of glass for double glazed panels)

2.4.2 Seriousness of Defects

In 2004, Chew and Silva (2004) conducted a survey, which 65 property managers who

are managing buildings with curtain wall are interviewed face-to-face. Objectives of the

survey are to find out the types defects in buildings’ curtain wall, as well as the

seriousness (rating) of such defects.

For the first part of his interview, he asks the property managers the average percentage

of area affected by the defects. In the second part the effectiveness of various “defects

quantifying factors” are asked before the property managers being requested to indicate

the seriousness of each defect in the building which is managed by him/her under these

quantifying factors. These quantifying factors and their respective mean ratings by the

property managers are shown in Table 2.4.1. The result shows that the main concerns of

the respondents towards curtain wall defects are the performance affected and the

possibility of defects forming other defects. It is noted that although “impact on the

performance” is ranked first, the mean rating each of the 4 factors do not vary greatly.

This shows that all of the importance of 4 defect quantifying factors is approximately

equal in indicating the defect seriousness.

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Factor Mean rating Rank

Ease of rectification 5.5 3

Behaviour of the environment - *

Impact on the performance 6.5 1

Stage when defect occurred - *

Tendency to aggravate the defect 5.3 4

Tendency to form another defect(s) 5.9 2

Table 2.4.1 The Ratings of Defect Quantifying Factors

Source: Chew, and Silva (2004)

For glass curtain wall and metal cladding, the results of defect ratings are shown in Table

2.4.2;

Wall Defect Rating

Cracking 69.6

Sealant failure 69.6

Water seepage 69.6

Vacuum layer failure 58.4

Sealant staining 46.4

Glass curtain wall

Dirt staining 28.5

Cracking 58.8

Sealant failure 58.8

Water seepage 58.2

Deflection 39.9

Chip off 34.6

Dirt staining 28.7

Metal cladding

Corrosion 28.7

Table 2.4.2 Results of Defect Ratings

Source: Chew and Silva (2004)

* Results of these factors are not shown in the paper

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From Table 2.4.2, it can be seen that in both of the glass panels and the metal claddings of

the curtain waling system, the most serious defects are cracking, sealant failure and water

seepage.

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2.5 Causes of Defects

2.5.1 Previous Studies - Type of Causes and their Contributions

In the following, the causes of defects studied or cited by Seeley (1987), Alves (1997)

and Chew, Tan and Kang (2004) are studied. In the study of Seeley (1987), the causes of

defects in the whole building are discussed. Causes of defects in the curtain wall are

specifically investigated by Alves (1997). The recent study of Chew, et al (2004) is

presented in order to review the views of curtain wall defects’ causes from various parties.

Seeley (1987) cites a research conducted by Building Research Establish (BRE). In this

BRE’s research, the total numbers of defects in the samples are recorded. The result of

the research is that the origins of buildings faults are design and specification, site and

materials, where the greatest origin was design and specification. The proportion of each

origin is shown in Fig. 2.5.1.

Design and Specification,

50%Site, 41%

Material and other, 8%

Fig. 2.5.1 The Result of BRE’s Research - Origins of Building Faults

Source: Seeley (1987)

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On the other hand, Alves (1997) cities a survey conducted within the building in the UK.

He reveals that the curtain wall failures are mainly attributed to workmanship, design and

supervision. The result is summarized in the Fig. 2.5.2.

Design, 22%

Workmanship, 35%

Low maintenance,

4%

Materials, 5%

Specification, 9%

Fabrication, 9%

Supervision, 16%

Fig. 2.5.2 Causes of Curtain Wall Failures

Source: Ledbetter, Harris (1997)

In order to composite technical evaluation index, Chew, et al (2004) studies into the

importance of various technical risk factors for occurrence of defects on curtain wall.

They have face-to-face interviews with building managers of 120 buildings and 25

building experts including architects, engineers, contractors, manufacturers, material

suppliers, as well as Building Maintenance Unit (BMU) specialists. The final composition

of the index which reflects the causes of curtain wall defaults is as shown in

Fig. 2.5.3 8.

8 The parameters used in the research and their results are attached in Appendix D

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Design, 38%

Construction, 4%Customer

Satisfaction#, 14%

Maintenance, 41%

Environment, 3%

Fig. 2.5.3 Composition of Chew’s Technical Evaluation Index

Source: Chew, Tan and Kang (2004)#

2.5.2 Classification of defects causes

From the above three studies (Seeley, 1987; Alves, 1997 and Chew et al, 2004), the

causes of defections of curtain wall are identified as below;

- Design faults (including specification)

- Construction faults (workmanship, site supervision and fabrication)

- Maintenance faults

- Environmental Impacts

For the environmental impacts, there are two types of them. The first one is impacts able

to be avoided by designers and property managers. It is proposed that the responsibility of

# Customer satisfaction is not considered as a cause of defects

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this kind of defect should be taken by designer and building managers. This will be

discussed in the “design” aspect. The second type is impacts that could not be avoided by

the designers or property managers. These impacts may deteriorate the curtain wall

system everyday. However, both parties could do nothing to avoid associated defects

from happening. Things could be done after the defects are occurred. This type of cause

will be regarded as “others causes”.

After identifying causes of curtain wall defects, in the next few chapters, various aspects

of curtain wall relating to these causes will be discussed. These aspects include design,

construction (or installation) and maintenance of the curtain wall. Other aspects which are

related to these causes will also be discussed in detail.

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2.5.3 Design

For design affecting the occurrence of defects, Hammad, Assaf and Shihah (1997)

construct a list of 35 design faults and asked the owners, A/Es and contractor to weight

them. The list of design faults and their weightings are shown in Table 2.5.1.

Table 2.5.1 Index and Ranks of Design Defects Source: Hammad, Assaf, and Shihah. (1997)

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Table 2.5.1 shows construction drawings group of faults was ranked highly by all three

parties while the architectural design group of faults received a low ranking by all.

Here are the most significant design faults according to different parties;

- Owners: inadequate structural design, ignoring access for maintenance equipment,

hiring unqualified designers and overlooking allowable load limits;

- Contractors: inadequate structural design, specifying incompatible exterior finishes

which need complete replacement and hiring unqualified designers;

- A/Es: hiring unqualified designers, inadequate structural design and insufficient

technical updating or staff training.

In the aspect of wind loading design, Hammad et al (1997) also show that all parties

ranked it very low. This finding agreed with the argument that wind code, as well as

code-making bodies is quite conservative (Robertson and See, 1998). Therefore, the wind

codes have fewer chances to be attributed to cause building defects.

For occurrence of glass breakage, Zhou (2002) mentions some possible causes. The first

one is glass being supported in wrong place. If the glass is supported at its edge or by a

hard/ sharp material, glass breakage may occur. It is because glass is usually weaker at its

edge. The second cause is the thermal stress. One of the causes of the thermal stress is

that one part of glass is directly under sunlight while the other part is rested in the shadow.

By such temperature difference between hot and cold parts, a stress thus is induced. If the

glass is already in high stress, it may exceed its ultimate stress because of this. Breakage

is thus occurred. It should be noted that above two causes could be prevented by

designers’ correct positioning of the supports, as well as correct calculation of forces

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acting on the glass. Therefore, the wrong points of support and excess thermal stress

should also be regarded as design faults.

Other studies (Chew, 2001; Zhou, 2002; Seeley, 1987 and Harris, 2001) also concern

about the imperfect design and fault design made by architects. In studying the

development of curtain wall, Chew (2001) points out that in earliest generation of curtain

wall system, certain limitations are present in its design. However, most of them were

improved in the second generation of curtain wall system. Table 2.5.2 shows their

limitations and improvements mentioned. Note that after the second generation, there are

fewer spaces for the improvement water-proof design.

Limitations of First generation

(Year 1800-1960)

Improvements in Second generation

(Year 1960-1980)

- Involves mainly in situ works which

requires high standard of

workmanship and quality control.

- Provides insufficient allowance for

moments due to temperature,

moisture, creep and differential

settlement. (See Fig. 2.3.14)

- Impossible to locate a leak because

of the lack of floor-to-floor flashing.

(See Fig. 2.5.4)

- Relies only on gaskets and sealants

to close all holes for water resistance.

- Using panels which are completely

finished at the factory with consistent

quality control.

- Reducing mullion’s deformation by using

separated mullions in panels.

- Applying water barrier between floors.

(See Fig. 2.5.5)

- Introduction of pressure equalization

system for water resistance.

Table 2.5.2 Limitations and Improvements of various Generations of Curtain Wall

System

Source: Chew (2001)

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Fig. 2.5.4 Moisture Moments from Floor to Floor without Flushing

Source: Chew (2001)

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Fig. 2.5.5 Water Barrier between Floors

Source: Chew (2001)

Other than the imperfect design of the whole curtain wall system, Zhou (2002) mentions

that imperfect design of a particular component will also preventing the curtain wall to

satisfy its performance. Zhou (2002) reveals that the aluminum beads for the fixing of

large glass panels are observed open-up during mock-up tests for windows. This “open-

up” effect will cause water leaking through the beads during typhoon.

In studying the causes of faulty design, knowledge and attitude of architects (or designers)

should also be discussed. For discussing the knowledge of architects, Seeley (1987) cites

a Building Establishment report found that architects sometimes had insufficient access to

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basic data such as British Standards. The attitude of architects towards their design is also

discussed by Seeley (1987). He implies that maintenance issues are usually not the

subject for thought before the erection of a building. Therefore, architects should regard

maintenance as an integral part of the design process. In addition, Willmott and Harris

(2001) point out architects may prefer their buildings be distinctive and every set of

interfaces is designed different from any previous building. The complexity of the facades

is thus increased and design faults are not uncommon. This also shows attitude of the

architects may be one of the causes of fault design.

In addition, low awareness of problems and poor communication links of designers with

other key project parties are also thought as faults of designers. For instance, Chew and

Tan (2002) argue that the staining of façade arising from design features could have been

solved by better communications. If architects’ awareness increases and the links are

strengthened, this possibility of occurrence of certain kinds of staining could have been

noticed by architect. Methods like rain run-off test or wind tunnel simulation experiments

could then be held thus the staining could be prevented.

Finally, in discussing the faults affecting the occurrence of defects, the boundaries of

design fault and construction fault may not be clear. An example given by Champion

(1999) is the difference in tolerances of frame and panels. If tolerances of the site-made

building frames are not related to the tolerances in the factory made curtain wall panels,

such difference is suggested not to be caused by quality of workmanship. Instead, it

should mainly be regarded as the consequence of design faults.

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2.5.4 Installation

As discussed in previous Chapter 2.5, possible faults in construction (“installation” for

curtain wall) should basically include workmanship, site supervision and fabrication. On

the other hand, similar to that of design faults, Hammad, Assaf and Shihah (1995) list out

the possible forms of construction defects. Using the list, a survey of contractors,

architectural/ engineering firms and owners is held. The 35 construction defects identified

as well as their resulted weightings are in Table 2.5.3.

Table 2.5.3 Index and Rank of Construction Defects Source: Hammad, Assaf, and Shihah (1997)

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Form Table 2.5.3, it can be seen that the “construction/inspection” group of defects are

ranked highly by contractors and architects/engineers. And here are the most significant

design defects according to different parties;

- Owners: hiring unqualified workforce, non-compliance with specifications, inability

to read drawings and insufficient site supervision;

- Contractors: non-compliance with specifications and hiring unqualified workforce;

- Architect/engineers: lack of inspection, neglect of the importance of inspection,

inability to read drawings, insufficient site supervision, poor communication between

owner and architect/engineer, multi-national construction experience and lack of

details.

Apart from above findings, Hammad et al (1997) also argue that large and complex

construction projects on tight completion deadlines may cause errors in construction.

In construction faults, similar to above, many studies regard most serious defects are

related to the workforce (Willmott and Harris, 2001; Tee, 2004; Ryan, 1994). The

workforce is blamed in two ways. The first one is its workmanship. Willmott at al (2001)

points out that installation error is usually blamed for the majority of façade failures. In

UK, the facades are constructed by largely uneducated and poorly trained workforce. In

addition to this, installers are also placed under time pressure. Sometimes they are

encouraged to put speed of installation for the top priority. This finding agrees with what

Hammad et al (1997) have argued. With these reasons, Willmott at al (2001) express that

workers are hardly fair to blame, although poor workmanship is a cause of façade failures.

Willmott at al (2001) pointed out that designers should have noticed this at the design

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stage. They should have designed the façade system which can be installed reliably in an

easy manner, as well as with high buildability.

On the other hand, Tee (2004) argues that the modern systems of curtain wall have been

improved and more tolerance to poor site workmanship. However, the poor site assembly

of the systems remains commonplace. Tee (2004) further gives an example that joint

systems were found incorrectly fitted. Poor weather-tight performance is as a result.

The second area being blamed is workforces’ site practice. Ryan (1994) says that the

glazing and claddings are not always being handled or stored properly. Local buckling of

claddings is caused.

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2.5.5 Maintenance Management

In maintenance management of the curtain wall, possible faults would appear so that the

occurrence of curtain wall defects may be affected. These possible faults in maintenance

are regarded as things related to maintenance preventing the façade from achieving its

predicted durability and serviceability. Opposite to well establishment of quality

maintenance, faulty maintenance will have great impact on the cost of future maintenance

works. If the performance of remedial treatment is not good, the chances of possibility of

recurrence will we increased (Chew et al, 2004).

Other than affecting the recurrence possibility, inadequate or improper maintenance may

spread or aggravate the defects. An example is given by Ryan (1994). It is an example of

loose fixings leading to ingress of water and corrosion around the fixing. Furthermore, if

water is allowed to enter through the fixing, the system will become damp leading to

further corrosion of the inner side. Another example is joints’ sealants not being replaced

in a suitable time. Although the direct cause of the sealants’ failure maybe the

environmental impacts, non-replacing of such broken sealant should be regarded as a

maintenance fault.

However, as mentioned before, nowadays maintenance is being budget driven. How

much maintenance work is to be done is not according to the actual need (Horner et al,

1997). At the same time, with the high maintenance costs sometimes result from design

faults or construction faults, the property managers could only do limited but inadequate

maintenance works.

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Not only the budget problem is faced by the property managers, O’Brien and Willmott

(2001) identify some others significant barriers to proper planned maintenance. They are

the lacking of an asset register, poor qualify of maintenance manuals and the lacking of

as-built drawings. They stress that with the lack of such asset register which identifies the

components, materials and systems making up the façade, maintenance trends to be on a

fire-fighting basis. They add that this will also cause maintenance falling behind the

minimum requirements that need to keep systems working properly.

Before studying the points which affect the quality of maintenance mentioned by Chew et

al (2004), the above items affecting the possibility of curtain wall damage are listed

below;

- performance of remedial treatment

- determination criteria of maintenance expense

- usage of asset register

- qualify of maintenance manuals

- availability of as-built drawings

For Chew, et al (2004), the quality of maintenance is also affected by maintenance

practice, maintenance competency and contractor competency. Factors affecting these

aspects are listed in Table 2.5.4.

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Table 2.5.4 Detail List of Factors Affecting Maintenance Practice, Maintenance

Competency and Contractor Competency

Source: Chew, Tan and Kang (2004)

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2.5.6 Other Causes

From some other studies (Loughran, 2003; Tee, 2004; Dalgliesh, 1998; Josey, 1997; Lee,

Wills and Wyatt, 1999; Chew, 1998; Chew, 1999; Willmott and Harris, 2001), other than

the causes related to design, installation and management of curtain wall, some other

activities are claimed to be the causes of curtain wall damage. They are damage caused by

nickel sulphide inclusion, wind debris, various environmental impacts and human actions.

2.5.6.1 Nickel sulphide inclusion

Inclusion of nickel sulphide is unavoidable for glass production. It puts tempered glass

highly at risk in spontaneous breakage. This phenomenon is widely described in various

papers and books (Loughran, 2003; Tee, 2004; Dalgliesh, 1998; Josey, 1997). When glass

is tempered, the nickel sulphide inclusions are modified into a form that grows and

transform with time and temperature. Small cracks may develop and penetrate into the

tension layer of glass. The spontaneous breakage of the glass thus may result.

2.5.6.2 Damage by wind debris

Wind debris’s impact on curtain wall is a kind of unavoidable environment impact.

Indeed, wind debris causing damage of building facades has been firstly being attached

importance to since 1994. In 1994, Hurricane Andrew hit Florida and caused serious

damages to building facades. In the same year, the debris impact standards were adopted

in the two Florida countries where the Hurricane Andrew affected most (Dalgliesh, 1998).

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In studying the impact of this cause to building façade, Lee et al (1999) presented a model

for the assessment of damage to building façade caused by windborne debris. They study

the conditions for flight and damage capability of potential objects that can become

“airborne missiles” in Hong Kong. In their study, potential objects that can become

“airborne missiles” are classified into three types, namely solid objects, sheet objects and

rods/ poles.

For solid objects, there are two sub-types of them. The first sub-type of solid objects is

particles lying on the ground such as dust, stones, litter, litter bins or building materials.

The other sub-type of solid object is attached particles. Advertisement hoardings, trees or

their branches, awnings and roof tiles are the example of attached particles. The second

type of debris is named sheet objects. Examples of them are sheets of corrugated iron or

plywood. For rods/ poles type of debris, they are rod-like materials such as fixing bolts,

bamboo poles, battens and 4”x 2” timbers.

In the study, Lee et al (1999) first identify the flight wind speeds9 of 3 kinds of object.

The flight wind speed is found to be varying with the type, material, size, density and

thickness of objects. Whether the objects being loosen or fixed also affects the flight

speeds. Solid objects are found to have the highest flight wind speed, while that of sheet

and rod objects are similar. After that, the damage capacities 10 of the objects are

calculated. Among 3 kinds of object, sheet objects have the highest damage capability.

Together with the relatively low flight wind speeds, sheet-like “missiles” pose the

greatest risk to modern claddings.

9 Flight wind speed of an object is the wind speed which causes an object starts to “fly” 10 Damage capacity of an object is the maximum force acting on the curtain wall by the object at the point(s) of impact

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To tackle the problem of wind debris damage, designers have to consider the sheet

objects’ damage capability when choosing the kind and thickness of glass for their

designs. Other than considering sheet objects’ damage capability in the design stage,

Dalgliesh (1998) also states some issues about tackling wind debris damage. They are the

adequacy of post-breakage behaviour of the curtain wall glass (as mentioned in the

Chapter 2.5.3 ) and the protection of the glass. For increasing the glass protection, he

suggests buildings should be glazed by glass protected by composite PET and PVB films

anchored to the frame. In non-hurricane regions, laminated glass and anchored panes are

suggested to be used.

2.5.6.3 Acid Rain

Because of the acidic nature of acid rain, acid rain is known to increase the rate of erosion

of metal. As in the curtain wall system, certain components are made of metal, acid rain

increases the rate of erosion of such components. Defined by Environmental Protection

Department, acid rain is defined as rain water’s pH value smaller than 5.6. Revealed by

Hong Kong Secondary Schools Acid Rain Survey 2002 organized by Hong Kong

Meteorological Society, the pH value of rain water in Hong Kong is mainly 5.7. However,

acid rain is found to appear in Yuen Long, Tuen Mun, Tsuen Wan, Kwai Chung, Kun

Tong, Tsueng Kuen O and Western District on Hong Kong Island. Revealed by the

survey, the main cause of acid rain is pollutants from Mainland’s factories. The exhausted

gases from power stations and cars are much minor causes of acid rain (except the acid

rain in Western District on Hong Kong Island).

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2.5.6.4 Other unavoidable environment impacts

In addition to wind debris, there are several unavoidable environment impacts. When the

curtain wall is exposing to the environment, certain chemical attacks or reactions may be

occurred. And these attacks and reactions will cause the curtain wall to deteriorate (Chew,

1999). Several examples are given by Chew (1998) in discussing the sealant failures of

curtain wall. For example, penetration of grit and debris into the sealants surface will

cause sealant intrusion. Other examples are ultra-violet radiation and ozone which cause

hardening of sealant. Photochemical degradation of the polymer will also soften the

sealant and/or cause the sealant to slump.

2.5.6.5 Damage by human

According to Willmott and Harris (2001), human damage can be classified into deliberate

damage and accidental damage. For curtain wall, deliberate damage is comparatively rare

and usually limited to glass breakage. An example is the case of Barometer11 in eastern

end of the Shepherd’s Bush Borough. The curtain wall of the Barometer was damaged by

people throwing a brick at it. Because of this, the Barometer had not been operated since

late 1998 (Loughran, 2003). To minimize the chance for deliberate damage, Willmott and

Harris (2001) suggest either resistant materials should be used or attacker should be

discouraged.

On the other hand, Willmott and Harris (2001) point out that accidental damage is mainly

caused by careless behaviour during cleaning and maintenance operations. For instance, a

11 A barometer is a device used for measuring air pressure. For the “Barometer” in Shepherd’s Bush Borough, it is a multi-storey scripture in curtain wall that measures and shows the air pressure of the city

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cleaning cradle which is allowed to swing against the façade could cause a substantial

damage. They add that even minor damage during operations could generate a significant

problem and affecting the performance of the façade. An example of this is joints being

carelessly left opened up after the maintenance operations and water is admitted into the

system.

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2.6 Conclusion

Because of numerous components in curtain walls, there are many possible curtain wall

defects. Moreover, because of numerous parties and activities involved in enclosing a

building with curtain wall, causes behind each defect are not easy to be found. Before

investigating the defect items as well as their causes in curtain walls of Hong Kong office

buildings, different literature on various aspects about curtain wall are reviewed. These

include factors affecting the chance of curtain wall defects’ occurrences (such as types

and components of curtain wall system) and activities involved in the life of a curtain

wall. Types and possible causes of curtain wall defects are also studied. All of the

information forms a basis of analyses in the later part of research.

From the previous literatures and studies, it can be concluded that poor curtain wall

design such as designing curtain wall requiring many in-situ works, choosing of non-

durable materials for components and using glazing bead as type of fixing method

employed is the major source of curtain wall defects. Compared to other aspects, various

requirements such as performance requirements, structural requirements and durability

requirements have to be strictly considered. On the other hand, the seriousness as well as

the incidence of curtain wall defects could not be found. Only a list of possible items

could be formed after the review. As the consequences caused by curtain wall defect

could be very serious, it is necessary to find out the incidence and seriousness curtain wall

defects, as well as the major causes behind the curtain wall defects in Hong Kong’s high-

rise office buildings.

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It should be noted that for the literatures reviewed, most of them are not studying the

curtain wall defects in Hong Kong. Also, as mentioned, the seriousness as well as the

incidence of curtain wall defects could not be found in the previous literatures or studies.

Therefore, in order to specifically find out defect items as well as their causes in curtain

walls of Hong Kong office buildings, a survey as well as 5 case studies is carried out in

various high-rise office buildings in Hong Kong.

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Chapter 3 – Research Design

Chapter 3

Research Design

3.1 Introduction

In this chapter, the research design of the Study is discussed. Rationale of choosing

particular types of research methods is illustrated. Moreover, how the data is collected

and analyzed is explained in the chapter.

3.2 Types of Research Methods

According to Yin (1994), there are 5 types of research method. They are experiment,

survey, archival analysis, history and case study. In each type of research method,

different ways of empirical evidence collecting and analyzing are utilized. The way of

how empirical evidence is collected or analyzed is based on the research method’s own

logic. Yin (1994) cites a table (Table 3.1) describing in what situations different research

methods should be used.

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Research method Form of research question Requires

control?

Focuses on

contemporary

events?

Experiment how, why Yes Yes

Survey who, what, where, how many, how much No Yes

Archival analysis who, what, where, how many, how much No Yes / No

History how, why No No

Case study how, why No Yes

Table 3.1 Relevant Situations for Different Research Methods

Source: Yin (1994)

In addition to the research method’s own logic, practical limitation of resources is also an

important factor in deciding the particular method(s) for a research.

3.3 Use of Research Strategies in the Study

In order to determine the research methods to be used for each part of this Study, the

nature of research questions being asked is looked into. As mentioned, this Study is

divided into 2 parts. The first part is finding the incidence and seriousness of curtain wall

defects in Hong Kong high-rise office buildings, while the second part is determining the

major causes of curtain wall defects in these buildings (as well as their effects on the

occurrences of curtain wall defects). Because in each of the 2 parts, the nature of research

questions asked is different, their research methods to be used should be considered

separately.

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Chapter 3 – Research Design In the part of finding the incidence and seriousness of curtain wall defects, the research

questions are

- “What are the incidences of curtain wall defects in Hong Kong high-rise office

buildings?”

- “How seriousness are the curtain wall defects in Hong Kong high-rise office

buildings?”

It is a “what” question for the first question, while the second question can be identified

as a “how much” question. From the Table 3.1, these research questions could be

answered only by the results of either a survey or an archival analysis. As this part of

research does focus on contemporary events of curtain wall defects, the research method

chosen for this part is survey. By using survey questionnaires, the statistical data of

incidences and seriousness of curtain wall defects could be collected from the population.

General incidences and seriousness of curtain wall defects among Hong Kong high-rise

office buildings could then be found.

In the part of determining the major causes of curtain wall curtain defects, the research

questions are

- “Why do curtain wall defects in Hong Kong high-rise office buildings occur?”

- “How do these causes of curtain wall defects affect the occurrence of curtain wall

defects in Hong Kong high-rise office buildings?”

- 89 -

Chapter 3 – Research Design For these 2 research questions, the first one is “why” question and the second one is

“how” questions. From the Table 3.1, these research questions could be answered by the

results of an experiment, a history and case studies. The reason behind this is that these

research methods (except “history”) enable the researcher to have direct contact to the

things studied, compared to the survey. However, the case studies are proposed to be used.

It is because unlike other 2 research methods, this part of research does focus on

contemporary events, while controls required in experiments are also difficult to find in

this Study.

For case study research, there are two types, including single-case study and multiple-

case studies. In this Study, latter type is used. The research questions of this part could be

answered by the qualitative and quantities evidences collected from the 5 cases studied.

3.3 Data Collection

3.4.1 Survey Part

The target respondents of this research are mainly Building Managers / Maintenance

Officers (written as “BMs/MOs” in below) of office buildings. BMs/MOs are chosen

because identify building defects and their respective causes is the duty of Building

Managers. According to Buildings Department (2002),

“the cause of the defect should be identified and eliminated to avoid recurrence of the

same defect (by the party who manage the building).” [with blanket added]

- 90 -

Chapter 3 – Research Design In addition, they usually participate in building maintenance of their responsible buildings

for years. Therefore, it is expected that BMs/MOs are the most detail, reliable and ready

accessible sources of information for this research. In order to find out the target

respondents, several actions are done by the author.

First, the high-rise office buildings in Hong Kong are identified by the author. In order to

achieve this, areas where high-rise office buildings located are found by studying satellite

maps of Hong Kong published in Lands Departments’ Hong Kong Guide 2006. After that,

the author travels downtown in person in order to observe and find out buildings with

curtain walls as building envelopes.

After finding out most high-rise curtain wall office buildings in Hong Kong, the author

uses two methods to identify their respective property management companies. The first

way is to find out by author recording the buildings’ property management companies in

person. This is done by either looking at tablets at the entrances, or direct enquiries to the

management staff. The second method is to look up the “Member List” on the website of

the Hong Kong Association of Property Management Companies Ltd (updated in late

2005). The first method is used for office buildings located along MTR lines and areas

near Yuen Long, while the second method is used for office buildings located in other

areas which are not accessible by MTR.

For the Survey part of the research, the author contacts the companies after finding out

the contact numbers of the companies. In order to ensure correct data could be collect

from respondents, before mass distribution of the questionnaire, the questionnaire is pilot-

tested and revised for two times. Pilot tests are done by each time sending questionnaires

- 91 -

Chapter 3 – Research Design to a small number of property management companies. Comments on the questionnaire

are then asked for. Questions being unclear to respondents are also asked to be indicated

by the respondents. As most of the names of Buildings Managers are unknown, in the

first phone call, the author asks the staff which department of the company would the

research related to. After knowing the department name, questionnaire(s) (together with

cover letters) are sent to companies by fax or by post. A follow-up phone call is made to

each company in order to ensure the questionnaires are distributed to respective

BMs/MOs of the identified office buildings. Until receiving returned questionnaire, the

author does not know if the Building Managers agree to participate in the research. It is

because most Building Managers are not stayed in companies’ head offices.

In the Survey Questionnaire, close-ended questions are asked. It is because the

questionnaire is only used for collecting quantitative data of the identified defects items.

Open-ended questions thus are not required.

3.4.2 Case Study Part

To find participants for the second part of the research (the Case Study part), respondents

of the Survey part are contacted by phone. All of them are invited to participate to the

Case Study part of research. Only respondents of the Survey part are invited because they

are expected to be being more interested in this research. Face-to-face interviews are

carried out in the Case Study. Other methods of interview are not used because of several

advantages of using face-to-face interview in this research. The first advantage is that

face-to-face interviews let the author to investigate the actual design of the curtain wall in

- 92 -

Chapter 3 – Research Design person during the interview. In addition to this, the neighborhood of the buildings, which

are relevant to the research, could also be studied through traveling to the site in person.

The Case Study Interview is a semi-structured interview. It can be divided into 4 parts.

The first part is asking open-ended questions about the design and maintenance of curtain

wall. For helping interviewees to identify the design of curtain wall, diagrams indicating

various types of curtain wall’s (and their components’) structural designs are shown to

them. Difficulties encountered in maintaining the building’s curtain wall are also asked.

The second part is to identify the causes of curtain wall defects by asking an open-ended

question first and then discussing items listed in Case Study Questionnaire. An open-

ended question is first asked for the sake of not setting boundaries to interviewees in

discussing defects causes. On the other hand, items listed in the Case Study Questionnaire

could introduce more possible causes to the interviewee. For some of these causes,

interviewees might have rarely considered before. With the open-ended question and

questionnaire, it is expected that interviewees give objective and complete answers of

defect causes. The chances of misunderstanding the items in questionnaire are also

reduced by author’s brief explanation to each item before asking interviewees to indicate

rankings. The third part is an open-ended question of difficulties encountered in curtain

wall defects’ rectification. This helps the author with finding out ways to decrease the

affect of curtain wall defects to the building. The fourth part of collection of data is just

collection of data related to curtain wall maintenance costs. There are main two purposes

in collecting such cost data. The first purpose is to collect more data for supporting

analyses in the Case Study part. Second purpose is to identify the amount of money spend

on repairing defects items, in order to supplement the discussion of seriousness of defects

items in the first part of research.

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Chapter 3 – Research Design The author expects that most Building Managers may not know details about what was

happened during installation of curtain wall. Therefore, other than BMs/MOs, the same

Case Study Questionnaire (together with a cover letter) is also faxed to each curtain wall

consultants and contractors for asking them to fill in. Two sources are used in finding

curtain wall consultants / contractors. The first one is Hong Kong Builder Directory,

which introduces material providers, service providers in various trades in the

construction industry. The second source is the “Member List” of Hong Kong Façade

Association (updated in 2005). The same method as that of property management

companies is used for contacting consultants / contractors after the contact numbers of

them are found.

3.5 Data Analysis

3.5.1 Survey Part

In the Survey part of research, 20 defect items (classified into 5 categories) are identified

from previous literature and relevant studies. For each defect item, quantitative

information including number of occurrence, frequency of repair and affected area of

curtain wall are collected. Numbers of them are added in order to investigate

quantitatively the seriousness of curtain wall defects generally in Hong Kong high-rise

office buildings. In addition, qualitative information is also collected. It is the general

impression on defects’ seriousness. For the sake of quantifying the defects, 4 defect

quantifying factors are used. Respondent are required to rank each of them for defect

items presence in their buildings. Rankings are averaged and used to study the seriousness

of curtain defect.

- 94 -


3.5.2 Case Study Part

On the other hand, 72 factors of possible defect causes are identified from previous

literature and related studies. They are grouped into 4 main categories in the questionnaire

of Case Study part of research. Together with the information collected through face-to-

face interviews, the discussion of curtain wall defects causes can be held. The data

collected from BMs/MOs and consultant / contractors are analyzed and discussed

separately.

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Chapter 3 – Research Design 3.6 Conclusion

Different strategies are used in the two parts of this Study. In the first part, survey strategy

is used. It is because by using survey questionnaires, statistical data of incidences and

seriousness of curtain wall defects could be collected from numerous Hong Kong high-

rise office buildings. For the second part, multiple-case studies strategy is used. It is

because the research questions of “why do curtain wall defects occur” and “how do these

causes affect the occurrences of curtain wall defects” could be answered by the

qualitative and quantities evidences collected from the cases studied.

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Chapter 4 – Survey Questionnaire

Chapter 4

Survey Questionnaire

4.1 Introduction

A Survey Questionnaire is used as an instrument in the first part of the Study in order to

collect data for analysis. In this chapter, how the Survey Questionnaire is constructed is

shown. The possible defects identified in the literature review are listed also. The method

of determining defects’ seriousness is discussed in the latter part of this chapter.

4.2 Construction of the Survey Questionnaire

4.2.1 Layout of the Survey Questionnaire

To introduce the background information to the target respondents, a questionnaire brief

is attached to the Survey Questionnaire. The questionnaire brief is shown in Appendix E.

In addition to introducing the background information, definition of terms in

questionnaire brief can help to avoid respondents from misunderstanding the questions.

For the survey questionnaire (see Appendix F), in order to fulfill the objective of

investigating the seriousness of curtain wall defects generally in Hong Kong high-rise

office buildings, it is divided into 3 parts. The first part contains questions asking 3 facts

and 1 general comment about each of the 20 defect items identified. The 3 facts include

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Chapter 4 – Survey Questionnaire number of defect occurrence, frequency of defect repairing and affected area of the

curtain wall. The general comment being asked for is the impression from Building

Manager on defects’ seriousness in their buildings. It is indicated by respondents ranking

the level of seriousness (1 = Very low, 4 = Very high). Before filling in the numbers and

rankings, the respondents are asked to indicate the record period of the data. Whether

certain components being absent in the design of curtain wall system is also asked.

In the second part of the survey questionnaire, respondents are asked to quantify

seriousness of defects by four defect quantifying factors identified by Chew and Silva

(2004). They include 1) tendency to aggravate the defect, 2) tendency to form another

defect, 3) ease of rectification, and 4) impact on the performance. If the presences of

particular defects are indicated in the first part, the respondents are required to quantify

these particular defects in the second part. For the factor “ease of rectification”,

respondents are asked to indicate which party (ordinary contractor, experienced

contractor or specialist contractor) is employed by them to rectify each defect. For the

factor of “impact on the performance”, respondents are asked to rank how great each

defect does affect curtain wall’s performance (with 1= Little, 4 = Extremely great). For

each of other 2 factors, respondents are asked to indicate the level of likelihood (1= Little,

4 = Extremely great) that defects are aggravated or forming another defect. The same

rating scale is used for each piece of qualitative information (including the impression

from Building Manager on defects’ seriousness, except “ease of rectification”) for the

sake of easy comparison with other qualitative information.

For knowing the details of the building, in the third part of the survey questionnaire,

respondents are requested to write down building’s information on the questionnaire.

- 98 -

Chapter 4 – Survey Questionnaire They include number of storey, age, as well as area covered by curtain wall of the

building. Contact person and contact method are also asked. It is done to enable the

author contacting the respondent directly. Through the third part of questionnaire, more

information is available in choosing cases for case studies. The task of inviting Building

Managers to participate the Case Study part is also much easier for the author.

4.3 Possible Defects Identified from Previous Literature

In order to 1) identify the curtain wall defects and 2) investigate the seriousness of curtain

wall defects generally in Hong Kong high-rise office buildings, items of possible defects

are identified. Because of the lack of previous comprehensive literatures and studies

focused on this specific topic, defects items are identified from various literatures and

studies. Literatures and studies about façade defects are reviewed.

Twenty possible defect items (as shown in Table 4.1) are identified eventually. They are

grouped under 5 categories according to the curtain wall components where these defects

may occur. These 5 categories are namely;

1) Glass panels

2) Aluminum panels

3) Fixings (including mullion, transoms, beads, embedment, etc.)

4) Sealants / Joints

5) Others

- 99 -


Category Possible defect items

1) Cracking

2) Shattering or falling off

3) Loosening Glass panels

4) Staining / decolouration, surface etching

1) Cracking

2) Falling off

3) Loosening

4) Staining / decolouration

5) Deformation

6) Separation, delaminating

Aluminum panels

7) Corrosion due to rain water, surface abrasion

1) Looseness

2) Missing parts

3) Corrosion Fixings

4) Damaged

1) Sealants / joints missing Sealants / Joints

2) Sealants / joints failure

1) Water seepage

2) Excessive air permeability / vacuum layer failure Others

3) Moisture behind curtain wall

Table 4.1 Possible Defect Items in the Survey Questionnaire

- 100 -

Chapter 4 – Survey Questionnaire 4.4 The Relative Seriousness of Defect Items

The seriousness of each defect items is determined using two types of information. The

first type is quantitative information and the other type is qualitative information.

Quantitative information is number of occurrence, frequency of defect repairing1 and

affected area of curtain wall filled in by the respondents. On the other hand, qualitative

information is the indicated levels of “general impression on defects’ seriousness” (in the

first part of the survey questionnaire) and 4 defect quantifying factors (in the second part

of the survey questionnaire) by the respondents. The final ranking of relative seriousness

of each defect item can be calculated when rankings of different defect items are known.

The weight of each factor used in the calculation is the same (as shown in Fig. 4.1), as all

of these factors are equally important in determining the relative seriousness of a defect.

Note that the amount of money spend on repairing defects items identified and discussed

in the Case Study part will be a supplement to the discussion of defects’ seriousness.

1 Note that this factor is discarded due to great variations in the qualities of the answers collected

- 101 -


No. of Defect, 14.30%

Area affected by Defect, 14.30%

Seriousness (in BM's impression),

14.30%Chance of

Aggravating Defect (Defect quantifying

factor 1), 14.30%

Chance of Spreading Defect

(Defect quantifying factor 2), 14.30%

Ease of Rectification


Impact on Performance


Fig 4.1 Weight of Each Factor used in the Calculation of Defects’ Seriousness

- 102 -

Chapter 4 – Survey Questionnaire 4.5 Conclusion

Twenty possible defect items are identified after the review of previous literatures and

studies. They are grouped under 5 categories, namely, “glass panels”, “aluminum panels”,

“fixings”, “sealants / joints” and “others”. For the seriousness of defect items, it is

determined by 7 factors including number of defects occurrence, frequency of repair,

affected area, respondents’ general impressions on defect seriousness and the 4 defect

quantifying factors.

- 103 -

Chapter 5 – Discussion of Survey Questionnaire Results

Chapter 5

Discussion of Survey Questionnaire Results

5.1 Introduction

In this chapter, the results of Survey Questionnaire are discussed. The rate of respond,

statistical data collected, as well as the implication of the results is discussed.

5.2 Description of Sample

Within a reasonable period of time, 23 out of 153 high-rise office buildings with curtain

wall identified could send back the Survey Questionnaires with data filled in. The

successful respond rate is 13.73%. The respond rate is low because of two reasons. The

first one is that several Property Management Companies claimed that the data required

in the Survey is sensitive. They would consider not to participate in the Survey according

to the policy of the companies. Building Managers / Operation Manager from 25 out of

153 buildings identified refused to participate in the Study with this reason. This occupies

16.33% of total population. The second reason is that Building Managers / Operation

Managers are busy and do not have time for participating in the Survey.

Because of incompletion, out of these 23 questionnaires, 2 were discarded in Part 1 and 1

was discarded in Part 2 of the Survey Questionnaire. Therefore, 21 complete Part 1

- 104 -


- 105 -

Survey Questionnaire and 22 complete Part 2 Survey Questionnaire remained for research

analysis.

5.3 Results of Survey Questionnaire

5.3.1 Seriousness of the Defects

In this section, the seriousness of the defect will be discussed in two aspects. The first

aspect is to find out the common type of defects in the buildings managed by the

respondents. The second aspect is the rankings and numbers filled in by the respondents.

5.3.1.1 Common type of defects

In order to find the common types of defect in Hong Kong high-rise office buildings, the

incidence of the defects are as shown in Fig. 5.1.

5 – Discussion of Survey Questionnaire Results

- 106 -

Incidence of Defects

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

1)

Crac

king

2)

Sha

tterin

g or fa

lling o

ff3)

Lo

osen

ing

4)

Stai

ning /

deco

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ion, s

urfac

e etch

ing1)

C

rackin

g2)

Fall

ing of

f3)

Lo

osen

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4)

Stai

ning /

deco

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ion5)

D

eform

ation

6)

Sep

aratio

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lamina

ting

7)

Corr

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due t

o rain

wate

r, surf

ace a

brasio

n1)

Lo

osen

ess

2)

Miss

ing pa

rts3)

C

orros

ion4)

D

amag

ed

1)

Sea

lants

/ joint

s miss

ing

2)

Sea

lants

/ joint

s fail

ure

1)

Wate

r see

page

2)

Exc

essiv

e air p

ermea

bility

/ vac

uum la

yer fa

ilure

3)

Mois

ture b

ehind

curta

in wall

Defect

% o

f num

ber o

f Bui

ldin

gs w

ith a

ssoc

iate

dC

ompo

nent

s ha

ving

suc

h D

efec

t

Main Categories of Defect: 1. Blue - Glass Panel 2. Grey - Aluminum Panel

3. Yellow - Fixing 4. Green - Sealant/Joint 5. Purple - Others

Fig. 5.1 Incidences of Curtain Wall Defects

Chapter


- 107 -

From Fig. 5.1, it can be observed that within 21 buildings, most of them encounter the

defect of water seepage. With this high percentage, water seepage is the most common

defect in high-rise office building. For the second, third and forth most common defect,

they are the moisture behind curtain wall, sealants/joints failure and glass panels falling

off. They are encountered by more than or equal to 60% of population. The high

incidence of moisture behind curtain wall may mainly due to small number of samples

having double glazed glass panels. In the 6 buildings which have double glazed curtain

wall glass panels, 4 of them encounter the problem of moisture forming behind curtain

wall. It should also be noted that for defects in fixings such as mullion, transom and

embedment, they are found to be the least common defect items.

5.3.1.2 Rankings of the Defects

Other than looking at defects’ incidences, the defect rankings made by respondent should

also be studied. Table 5.1 shows the mean values and mean scores of different defect

items.


- 108 -

Defect quantifying factors No. of

Defect/yr* No. of Defect

/floor/yr Area affected

by defect

Seriousness (in BM's

impression) Aggravate

Defect Spread Defect

Ease of rectificat'n

Impact on Perform.


Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD1) Cracking 37.941 147.449 0.065 0.144 1.000 0.000 1.222 0.548 1.353 0.493 1.412 0.507 2.765 0.437 2.813 1.1672) Shattering or falling off 4.941 11.513 0.025 0.038 1.000 0.000 1.444 0.784 1.200 0.414 1.267 0.458 2.867 0.352 3.143 1.0273) Loosening 0.471 1.007 0.019 0.045 1.000 0.000 1.167 0.514 1.286 0.469 1.429 0.514 2.857 0.363 3.000 0.816

Glass panels

4) Staining / decolouration, surface etching 8.059 28.902 0.380 1.450 1.111 0.471 1.278 0.575 1.467 0.516 1.400 0.507 2.800 0.414 2.500 1.092

1) Cracking 0.500 0.905 0.022 0.041 1.000 0.000 1.000 0.000 1.308 0.480 1.385 0.506 2.538 0.776 3.000 1.1832) Falling off 0.667 1.435 0.030 0.065 1.000 0.000 1.000 0.000 1.231 0.439 1.231 0.439 2.538 0.776 3.417 0.9963) Loosening 0.583 1.165 0.026 0.053 1.000 0.000 1.000 0.000 1.462 0.519 1.538 0.519 2.692 0.480 3.000 0.8534) Staining / decolouration 3.750 10.805 0.183 0.542 1.308 0.855 1.385 0.650 1.429 0.514 1.357 0.497 2.714 0.469 2.385 1.1935) Deformation 4.750 9.498 0.035 0.040 1.083 0.289 1.231 0.439 1.385 0.506 1.385 0.506 2.538 0.776 2.583 1.1656) Separation, delaminating 0.500 0.674 0.025 0.033 1.083 0.289 1.154 0.376 1.308 0.480 1.308 0.480 2.923 0.277 2.583 1.165

Aluminum panels

7) Corrosion due to rain water, surface abrasion 4.000 10.745 0.188 0.541 1.615 1.325 1.385 0.768 1.500 0.519 1.786 0.699 2.714 0.469 2.538 1.127

1) Looseness 0.706 1.404 0.031 0.064 1.118 0.485 1.111 0.323 1.385 0.506 1.692 0.947 2.846 0.376 2.750 1.0552) Missing parts 0.235 0.752 0.008 0.033 1.000 0.000 1.056 0.236 1.385 0.506 1.692 0.947 2.846 0.376 2.917 1.1653) Corrosion 0.882 1.833 0.041 0.081 1.294 0.985 1.222 0.548 1.462 0.519 1.615 0.650 2.538 0.776 2.333 1.231

Fixings

4) Damaged 0.235 0.970 0.011 0.044 1.059 0.243 1.111 0.323 1.385 0.506 1.615 0.650 2.692 0.480 2.583 1.0841) Sealants / joints missing 0.118 0.485 0.005 0.022 1.118 0.485 1.167 0.514 1.462 0.660 1.769 1.013 2.462 0.776 2.667 1.231Sealants /

Joints 2) Sealants / joints failure 48.118 124.483 0.088 0.140 1.222 0.548 1.611 0.608 2.059 0.966 2.235 1.147 2.588 0.712 2.813 1.1091) Water seepage 36.125 123.775 0.125 0.158 1.389 1.037 1.611 0.916 2.000 0.943 2.368 1.116 2.789 0.419 2.833 1.0432) Excessive air permeability / vacuum layer failure

9.600 17.344 0.058 0.136 1.083 0.289 1.083 0.289 1.385 0.506 1.385 0.506 2.846 0.376 2.750 1.138Others

3) Moisture behind curtain wall 4.600 2.702 0.146 0.140 1.083 0.289 1.083 0.289 1.357 0.497 1.357 0.497 2.786 0.426 2.615 1.121

* Factor discarded due to large standard deviation Table 5.1 Mean Number / Score of Defects

Chapter

Chapter 5 – Discussion of Survey Questionnaire Results From Table 5.1, it shows that one of the factor that will be used to determine the

seriousness of defects, various greatly. It is the “No. of Defect /yr” which shaded in grey

as shown in Table 5.1. In particular defects, the values of standard deviation are about 4

times of the defect mean numbers. It is because in particular buildings, the number of

stories is very great compared with others. Therefore, a column of “No. of Defect

/floor/yr” has been added to test if the variation could be improved after the number of

defect in each building is divided by the its number of stories before averaging the results

with other buildings. According to Table 5.1, although the standard deviation still quite

large, the extreme variations have been improved. In view of this, in determining the

seriousness of defect, the factor “No. of Defect /yr” is discarded. A new factor, “No. of

Defect /floor/yr” will be used instead. Another special note to Table 5.1 is that only factor

“Ease of rectification” has 95% of its mean score above 2.5, where there are only three

values of rank (1, 2 and 3) for the respondents to choose.

In order to compare the seriousness of defects, ranks of scores of different defects are

listed in Table. 5.2.

- 109 -


Sub - Ranking Defect quantifying factors


No. of Defect

/floor/yr

Area affected

by defect


impression)Aggravate

Defect Spread Defect

Ease of rectificatn

Impact on

Perform.1) Cracking 7 14 8 15 11 10 7 2) Shattering or falling off 14 14 3 20 19 2 2

3) Loosening 17 14 10 18 10 3 3 Glass panels

4) Staining / decolouration, surface etching

1 8 6 4 12 7 18

1) Cracking 16 14 18 16 13 16 3 2) Falling off 12 14 18 19 20 16 1 3) Loosening 13 14 18 5 9 13 3 4) Staining / decolouration 3 3 4 8 16 11 19

5) Deformation 10 9 7 9 13 16 14 6) Separation, delaminating 14 9 12 16 18 1 14

Aluminum panels


2 1 4 3 3 11 17

1) Looseness 11 6 13 9 5 4 10 2) Missing parts 19 14 17 9 5 4 6 3) Corrosion 9 4 8 5 7 16 20

Fixings

4) Damaged 18 13 13 9 7 13 14 1) Sealants / joints missing 20 6 10 5 4 20 12 Sealants /

Joints 2) Sealants / joints failure 6 5 1 1 2 15 7

1) Water seepage 5 2 1 2 1 8 7 2) Excessive air permeability / vacuum layer failure

8 9 15 9 13 4 10 Others

3) Moisture behind curtain wall

4 9 15 14 16 9 13

Table 5.2 Rankings of Defects’ Mean Number / Score

In Table 5.2, the higher the ranking (e.g. “1” and “2”), the more serious is the defect in

view of the respective factor. To give a more obvious result, overall rankings are

established in Table 5.3 by adding up 7 rankings in each of the rows in Table 5.2.

- 110 -


- 111 -

Category Possible defect items Sum of Sub-ranking

% difference from 1st

Rank's Total Score

Overall Ranking


impression)

1) Cracking 72 177% 9 6 2) Shattering or falling off 74 185% 10 6 3) Loosening 75 188% 12 6 Glass

panels 4) Staining / decolouration, surface etching

56 115% 4 5

1) Cracking 96 269% 19 18 2) Falling off 100 285% 20 18 3) Loosening 75 188% 12 18 4) Staining / decolouration 64 146% 6 3 5) Deformation 78 200% 15 16 6) Separation, delaminating 84 223% 17 6

Aluminum panels


41 58% 3 2

1) Looseness 58 123% 5 12 2) Missing parts 74 185% 10 16 3) Corrosion 69 165% 8 6

Fixings

4) Damaged 87 235% 18 12 1) Sealants / joints missing 77 196% 14 6 Sealants /

Joints 2) Sealants / joints failure 37 42% 2 3 1) Water seepage 26 0% 1 1 2) Excessive air permeability / vacuum layer failure

68 162% 7 12 Others

3) Moisture behind curtain wall 80 208% 16 12

Table 5.3 Overall Rankings of Defect Seriousness

As shown in Table 5.3, the most serious defect in curtain wall is “Water Seepage”. To

study which defect items is closely behind the 1st rank defect, the percentage difference

form 1st rank’s sum is calculated in Table 5.3. A more clear presentation of the figure is

by Fig. 5.2. Note that the top 6 highest ranks of the “overall ranking” are agreed with that

of the “Defects’ Seriousness in Building Managers’ impression”. This proves the

reliability of the result.


- 112 -

Top 3 Most Serious Defects

0%

50%

100%

150%

200%

250%

300%

1)

Crac

king

2)

Sha

tterin

g or fa

lling o

ff3)

Lo

osen

ing

4)

Stai

ning /

deco

lourat

ion, s

urfac

e etch

ing1)

C

rackin

g2)

Fall

ing of

f3)

Lo

osen

ing

4)

Stai

ning /

deco

lourat

ion5)

D

eform

ation

6)

Sep

aratio

n, de

lamina

ting

7)

Corr

osion

due t

o rain

wate

r, surf

ace a

brasio

n1)

Lo

osen

ess

2)

Miss

ing pa

rts3)

C

orros

ion4)

D

amag

ed

1)

Sea

lants

/ joint

s miss

ing

2)

Sea

lants

/ joint

s fail

ure

1)

Wate

r see

page

2)

Exc

essiv

e air p

ermea

bility

/ vac

uum la

yer fa

ilure

3)

Mois

ture b

ehind

curta

in wall

Defect

% d

iffer

ence

from

1st

Ran

k's

Tota

l Sco

re

Top 3

Main Categories of Defect: 1. Blue - Glass Panel 2. Grey - Aluminum Panel 3. Yellow - Fixing 4. Green - Sealant/Joint 5. Purple - Others

12

3

Fig. 5.2 Top 3 most Serious Defects in Curtain Wall

Chapter

Chapter 5 – Discussion of Survey Questionnaire Results In Fig. 5.2, it can be observed that there are 2 defects closely follow the utmost serious

defect. In addition, they are all within the 60% boundary line as shown in Fig. 5.2 (the red

line). The ranking of 4th rank defects’ cause is with 120% difference to that of the 1st rank,

which is already a very great percentage difference compared to the top 3 ranks. In view

of this, together with “Water Seepage”, these three defects are called “Top 3 Most Serious

Defects” and will be discussed in detail. To sum up, the Top 3 most Serious Defects are,

- Water seepage

- Sealants / joints failure

- Corrosion of aluminum panels due to rain water

Fig. 5.3 shows the composition of the “Top 3 most Serious Defects”.

Compositions of Top 3 most Serious Defects

5

6

2

2

5

1

1

1

4

2

1

3

1

2

3

8

15

11

7

7

17

0 5 10 15 20 25 30 35 40 45

Water seepage

Sealants / jointsfailure

Corrosion ofAluminum panelsdue to rain water,surface abrasion

Def

ects

Sum of Ranking / Ranking ( 1 = the most serious defect)

No. of Defect /floor/yr

Area affected by defect

Seriousness (in BM'simpression)

Defect quantifying factor 1 -Chance of Aggravting Defect

Defect quantifying factor 2 -Chance of Spreading Defect

Defect quantifying factor 3 -Ease of rectification

Defect quantifying factor 4 -Impact on Performance

Fig. 5.3 Compositions of Top 3 Most Serious Defects

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Chapter 5 – Discussion of Survey Questionnaire Results From Fig. 5.3, it can be seen that in the top two ranks, they are ranked highly in all factors

except in “Ease of Rectification”. It is mainly due to the fact that most of the respondents

highly rank this factor. Therefore, great differences in ranking may be resulted from small

variations in the sums of Sub-ranking. For the defects of “Corrosion of aluminum panels

due to rain water”, although its impact on performance is not great, it is still in the 3rd

most serious defect.

On the other hand, in Fig. 5.2, structural defect items like “Loosening”, “Falling off”and

“Cracking” of glass panels, aluminum panels as well as fixings, have relative less serious

compared to other types of defect.

5.4 Implications of the Results

5.4.1 Most Defects are Rectified by Specialist Curtain Wall Contractors

As mentioned, Table 5.1 shows that the factor “Ease of rectification” has most of its mean

score above 2.5. This means that most respondents think that all defects in curtain wall

require specialist curtain wall contractors’ rectification, regardless of the seriousness and

type of the defects. Therefore, remediation of curtain wall defects is quite stringent and

very different from that of other building defects.

5.4.2 Curtain Wall in Hong Kong are generally Structurally Safe

From the data given by Building Managers, especially for fixings’ defects, medium to

low incidences as well as low seriousness are generally found in structural defects. Even

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Chapter 5 – Discussion of Survey Questionnaire Results it is quite common for glass panels to fall off (as shown in Fig. 5.1), its seriousness is not

very high (as shown in Fig. 5.2). Therefore, it is believed that curtain wall in high-rise

office building are generally structurally safe. The relative low overall ranking of the

structural items also expresses that the main concern to the respondents in curtain wall

maintenance is not structural defects. Moreover, this shows that both curtain wall design

and installation in Hong Kong are so mature that with certain level of maintenance,

having a curtain wall as the building’s envelope could be very safe. It is expected to be

one of the reasons why curtain wall is widely used as envelopes of high-rise office

buildings.

5.4.3 More Non-structural Defects identified in Aluminum Panels

Compared to glass panels and fixings, there are more non-structural defects (e.g.

decolouration, corrosion) found in aluminum panels. It can be reflected by the high

incidences of aluminum panels’ defects found in Fig. 5.1 and 3rd ranked seriousness of

“corrosion of aluminum panels due to rain water”. It can be explained with two possible

reasons. The first one is that defects of aluminum panels are the easiest to be seen than

that of glass panels and fixings. Aluminum panels, usually light grey in colour, are less

able to “hide” defects than glass panels having shiny surface coatings. For the fixings,

they can also “hide” defects by their dark colour in usual. The second reason is that acid

rain mainly harms metal components of curtain wall. It is well-known that acid rain

enhances the corrosion of metals. Therefore, deterioration of aluminum panels is more

seriousness than glass panels in industrial or high traffic areas where acid rains are

formed. Fixings seem to be less harmed either because their corrosion is “hidden”, or

because they are well-hidden under glass panels in some new curtain wall designs.

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Chapter 5 – Discussion of Survey Questionnaire Results 5.4.4 Serious Water Seepage

As a common defect (as shown in Fig. 5.1) as well as the 1st ranked serious defect (as

shown in Fig. 5.2), water seepage in curtain wall is found to be the most serious. Indeed,

either in residential or office buildings, water seepage always is a common building

defect. In well-built residential buildings, it usually occurs only after a long period of

occupation. However, in the Survey, it is found that even for office buildings completed

within 5 years, water seepage occurs in curtain wall. However, this is regarded as

“normal” by Building Managers. Relatively serious water seepage found in curtain wall is

mainly because curtain wall is composed of numerous components. Therefore, a curtain

wall has more weak points to water seepage than a building envelope made of concrete.

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Chapter 5 – Discussion of Survey Questionnaire Results 5.5 Conclusion

Based on the Survey Questionnaire results, it is found that within 21 high-rise office

buildings, water seepage is the most common defect. Other defects such as moisture

behind curtain wall, sealants/joints failure and glass panels falling off are also having high

incidence. For the seriousness of the defects, based on the 7 seriousness determining

factors, “Top 3 most Serious Defects” are found. They include water seepage, sealants /

joints failure and corrosion of aluminum panels. In addition, four implications based on

the questionnaire results are stated. First, it is found that most defects in curtain wall are

rectified by specialist curtain wall contractors. Second, curtain walls in Hong Kong are

generally commented to be structurally safe. Third, more non-structural defects identified

in aluminum panels is mainly due to acid rain and the light colour of the panels. The last

implication is that serious water seepage is result mainly because curtain walls have many

weak points to water seepage.

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Chapter 6 – Case Study Questionnaire

Chapter 6

Case Study Questionnaire

6.1 Introduction

During each face-to-face interview with Building Manager, a Case Study Questionnaire is

used as an instrument in to collect data for analysis. In this chapter, how the Case Study

Questionnaire is constructed is shown. The possible defects’ causes identified in the

literature review are listed also.

6.2 Construction of the Questionnaire

6.2.1 Layout of the Questionnaire

Similar to that of the Survey part, in order to introduce the background information and

enhance the understanding of questions to the target respondents, a questionnaire brief is

attached to the Case Study Questionnaire. The questionnaire brief is shown in

Appendix E.

For the Case Study questionnaire (see Appendix G), in order to fulfill the objective of

investigating the causes of curtain wall defects in chosen office buildings, it is divided

into 3 parts. The first part is an open-ended question as stated below;

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“What are the causes of curtain wall defects in the building that you are managing?”

The answer provided by Building Managers is recorded in the questionnaire. After that,

the 72 items of possible defects’ causes about design, installation and maintenance of

curtain wall are presented in the questionnaire. Interviewees are asked to rank how great

each possible cause in the list does affect curtain wall defects’ occurrences (1= Does not

affect, 5 = Strongly affects). As it is expected that Building Managers do not participate

in design or installation of curtain system, an “unknown” column is provided. However,

regardless of this, a full list of 72 items is presented to them. It is because certain causes

(e.g. workmanship) could be identified during the rectification works (Seeley, 1987), or

simply by observing the “final output” – the installed curtain wall. The third part of case

study questionnaire is blank spaces for interviewees to add defects’ causes other than

what have been listed in the questionnaire. Similar to the listed causes, rating of these

“new” causes are also required. This part is set in case of other causes could be identified

by the interviewees.

6.3 Possible Causes of Defects Identified from Previous Literature

In order to find out the causes of curtain wall defects, items of possible defects causes are

firstly identified. Similar to that of Survey part, there is a lack of previous comprehensive

literatures and studies focused on this specific topic. Therefore, defects causes are

identified from various literatures and studies. Below are the topics of literatures and

studies about façade defects reviewed by the author.

- condition assessment and defects of building façade

- design faults relating to defects

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- construction faults relating to defects

- management faults relating to defects

Seventy-two possible defects’ causes related to curtain wall (as shown in Table 6.2) are

selected after the review. They are grouped under 4 main categories and 19 sub-categories.

The 4 main categories are namely;

1) Design

2) Construction (or Installation)

3) Maintenance

4) Others

I. Design

Civil design

- Inadequate provisions for movement

- Ignoring aggressive environmental

effects

- Ignoring biological effects

- Inadequate structural design

- Ignoring load impact on structural

stability

- Exceeding allowable deflection limits

- Ignoring wind effects on the structure

Architectural design

- Specifying incompatible exterior finishes

with the climate

- Ignoring climatic effects on exterior

shapes

- Designing inadequate joints between

finished surfaces

- Architects’ insufficient access to basic

data such as British Standard

- High complexity of curtain walling

system design

- Inadequate communication between

designer and other key project parties

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Maintenance practicality and adequacy

- Ignoring access for maintenance

equipment

- Designing permanent fixations

- Ignoring maintenance equipment

availability

- Ignoring maintenance requirements in

the design

Construction materials

- Thermal movement in different material

- Selection of materials unsuitable for

climatic conditions

- Use of non-durable materials

Construction specifications

- Unclear specifications

- Inadequate definition of material type

- Overlooking QA/QC construction

procedures

- Specifying inadequate mix design

Consultant firm administration and staff

- Lack of QA/QC programme during

design

- Insufficient technical updating or staff

training

- Hiring unqualified designers

- Lack of designer field experience

- Lack of designer’s technical background

- Designer ignorance of material

performance

- Misjudgement of climatic conditions

Construction drawings

- Lack of references

- Conflicting details

- Lack of details

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II. Construction

Construction inspection

- Lack of inspection

- Hiring unqualified inspectors

- Neglect of the importance of inspection

- Not implementing corrective actions

during job execution

Contractor administration

- Non-compliance with specifications

- Large and complex construction project

on tight completion deadline

- Hiring unqualified workforce

- Inability to read drawings

- Insufficient site inspection

- Poor communication between the owner

and architect/ engineer

- Hiring unqualified supervisors

- Multinational construction experience

Workforce’s practice and performance

- Poor site assembly of the system

- Use of expired materials

- Poor material handling and storage

Construction equipment

- Wrong use of equipment

- Inadequate performance of equipment

- Lack of required amount of equipment

Construction drawings

- Lack of references

- Lack of details

- Conflicting details

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III. Maintenance

Maintenance practices

- Non-compliance to specified cleaning

methods and equipment

- Inadequate frequency of maintenance

- Budget constrain of maintenance

expense

Maintenance competency

- Maintenance staff lack of relevant

experience

- Inadequate quality of supervision

- Inadequate qualify of maintenance

manuals

Remedial contractors competency

- Inadequate quality of remedial work

- Long responses time

- Long restoration and repair time

- Inadequate standard of workers’ skill set,

qualification and experience

Information Problem

- Lack of asset register providing

components, materials and system

making up curtain walling system

- Lack of as-built drawings

IV. Other Causes

Damage my human

- Deliberate damage

- Accidental damage

Damage by wind debris

Table 6.1 Possible Defects’ causes listed in the Case Study Questionnaire

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6.4 The Rating of Causes of Defects

For defects’ causes, their relative ratings are determined using only qualitative

information. The information relayed on is the numerical scores of different defects’

causes indicated by the respondents. Relative importance of each defects’ cause is known

when the scores of different defects’ causes are compared.

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6.5 Conclusion

The Case Study questionnaire is divided into 3 parts. The first part is an open-ended

question asking the causes of the occurrences of curtain wall defects in interviewees’

buildings. The second part of the questionnaire is the list of 72 items of possible defects’

causes identified after the review of previous literatures and studies. These causes are

grouped under 4 main categories and 19 sub-categories. The 4 main categories are

“design”, “construction”, “maintenance” and “others”. For the third part of the

questionnaire, it is blank spaces for interviewees to add defects’ causes other than what

have been listed in the questionnaire.

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Chapter 7 – Case Study Findings Analysis and Discussion

Chapter 7

Case Study Findings Analysis and Discussion

7.1 Introduction

This chapter is divided into 3 parts. In the first part of this chapter, the case study design

is introduced. In the second part, data collected from the questionnaire in each building

studied or company interviewed is separately analyzed and discussed. The combination of

analysis and discussion is due to the fact that during the result discussion of each building

(or company), quick referencing to the data collected in the Case Study Questionnaire is

required. After the results of buildings are analyzed and discussed separately, general

discussions comparing the results under the groups of “Cases of Building” and

“Consultant / Design Company” buildings” are held.

In the discussion of result of each building, following issues are aimed to be investigated:

- Major causes of curtain wall defects in the case studied

- Affect of the identified curtain wall defects’ causes on defects

The second issue is raised because some defects’ causes identified in the literatures do not

regarded as factors directly causing curtain wall defects by the interviewees. Instead, they

are regarded as factors that worsen the effect of defects on curtain wall.

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7.2 Case Study Design

7.2.1 Focus

The case studies focus on the assessment of factors affecting the occurrences of curtain

wall defects in high-rise office buildings in Hong Kong. Another focus is to find out

factors worsening the effect of curtain wall defects on the building.

7.2.2 Reasons for Choosing the Cases

Five out of 21 buildings are chosen for the Case Study part. They are chosen because they

are the buildings which Building Managers offered full support to the research. In

addition, relatively quick responses they are in sending back the questionnaires as well as

accepting the case study’s invitations. With sufficient information, data support, as well

as time for analyzing the data, better research result could be reached by the author. The

buildings studied in the research are namely Building no.1, Building no.2, Building no.3,

Building no.4 and Building no.5.

7.2.3 Case Study Data Collection Method

As the buildings chosen are the buildings which Building Managers have filled in the

Survey Questionnaire and sent back to the author, the general situations of curtain wall

defects in the buildings are known by the author. This provides buildings’ general

information which is important for the Case Study part. In addition, in collecting the data

specifically for Case Study part of research, Building no.1, Building no.2, Building no.3,

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Building no.4, and Building no.5 agreed to provide information by site visits, face-to-face

interviews and follow-up phone interviews. In the face-to-face interviews, Building

Managers / Maintenance Officers (written as “BMs/MOs” in below) agreed to provide

information by a case study procedure as stated from 7.2.3.1 to 7.2.3.5. After the face-to-

face interviews, site visits to the curtain walls by the author (accompanied the BMs/MOs)

are agreed by 2 out of 5 BMs/MOs. Photos are taken in such site visits. Therefore, in the

research, both methods of direct and indirect observation are used.

7.2.3.1 Identifying the Design of Curtain Wall

In this session, the BMs/MOs are asked to identify the type of curtain wall, material,

joint and the method used in fixing panels onto the frame (for curtain wall with stick

system only). These areas may affect the structural performance and the chance of water

seepage of the curtain wall.

7.2.3.2 Collecting Information of Curtain Wall Maintenance

Types of management for curtain wall and difficulties encountered in managing curtain

wall are answered by the BMs/MOs in this session.

7.2.3.3 Reviewing the Defects

In the Survey Questionnaire, most buildings have the problem of water seepage.

Therefore, sealant failure’s type that can reflect the cause of defect is identified by the

BMs/MOs. Fig. 2.4.1 is shown to the BMs/MOs.

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7.2.3.4 Discussing Defects’ Causes

For discussing the defects’ causes, an open-ended question about the causes of curtain

wall defect in the building they managed is answered by the BMs/MOs. After this, the

BMs/MOs agreed to provide information by marking the level of effect of possible

defects causes on curtain wall defect of their building. These causes are listed in a preset

questionnaire which is presented in English.

7.2.3.5 Collection of Maintenance data

Lastly, maintenance data are agreed to be answered by the BMs/MOs. They are 1) the

ratio of spending on each curtain wall defect to other certain wall defects; and 2) the

percentage of total spending on curtain wall defects on total building maintenance cost.

These data are asked to indicate the seriousness of defect quantitatively.

7.3 Case Study Questionnaire Results Analysis and Discussion

7.3.1 Building no.1

7.3.1.1 Information and data of Building no.1

Building no.1 is one of the high-rise office buildings located in Wan Chai facing the

Victoria Habour. Its number of storey is over 50 and it also could be regarded as “super

high-rise building”. The age of this building is “10-15 years”. All four sides of building

are enclosed by curtain wall. Table 7.1 shows its curtain wall design as well as the general

situation of curtain wall defects in the building.

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Type of curtain wall Stick System

Type of Joint Drainage Joint

Type of glass fixing Glazing Bead

Materials Heat-strengthened glass, Double glazing,

Aluminum fixings

Glass Breakage (no. /yr) 0.500

(610 at York 1999)

Sealant failure (no. /yr) 38.461 (type: normal weathering)

Water Seepage (no. /yr) (mostly

associated with sealant failure)

38.461

Repair cost of

glass breakage : sealant : fixing

1:1:0

% of total repair cost in curtain wall

defects on total maintenance cost

<1% (3% if York’s damage included)

Other Defects (no. /yr) Staining : 0.160

Vacuum layer failure : 3.077

Maintenance - Scheduled maintenance

- Corrective planned maintenance


of Building no.1

In Table 7.1, it should be noted that in normal circumstances, glass breakages are not

serious (in terms of number affected, the same as below) for the building. However, in

Typhoon York in 1999, 610 pieces of glass panels are broken. For the defect of sealant of

sealant failure and water seepage, they are quite serious. Reasons of them could be

explained in 7.3.1.2

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For the curtain wall maintenance of Building no.1, it is identified as scheduled maintenance plus corrective planned maintenance. In every 5 years, the whole curtain wall system is

checked by specialists. Price quotation of curtain wall rectification contractors is done

yearly. In order have glass breakages being repaired promptly as well as for lowering

panel acquisition cost (by bulk sale), spare packages of glass panels are stored. Altogether,

there are 500 pieces of glass panel (at least 1 for each type of glass panel) being ready for

broken glass replacement if glass breakage appears.

7.3.1.2 Major Defects’ Causes of Building no.1

As shown in Table 7.6, the highest ranks in defects’ causes marked by the Maintenance

Officer of Building no.1 are “(Others) Damage by wind debris”, “(Construction) Large

and complex construction project on tight completion deadline”, and “(Design)

Thermal movement in different material”. Damage caused by wind debris could be

reflected by the 610 pieces of glass panels damaged in Typhoon York in 1999. In 2000, a

wind tunnel test is employed to identify the cause of such damage. The report of the test

stated that curtain wall of Building no.1 is mainly damaged by wind debris, but not by

glass panels incapable to withstand high forces of wind. Although the type of wind debris

is not clearly stated in the report, the Maintenance Officer believes that the damage is

caused by broken glass in tempered glass (forming numerous of debris upon its breakage;

Josey, 1997) curtain wall buildings nearby.

The second major defects’ cause identified by the Maintenance Officer is poor

workmanship in sealant application. According to the Maintenance Officer, the thickness

of the sealant should be normally 20-25mm for a curtain wall system. However, in areas

where water seepage occurs, the sealant was found to be only 10mm in thickness. He

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believes that poor workmanship is due to large and complex construction project on tight

completion deadline. Indeed, the super high-rise building was completed within 4 years.

Average time of construction for each floor is approximately 4 days (claimed by the

developer). This agrees with the finding of Willmott at al (2001) and Hammad et al (1997)

that poorer workmanship could be resulted if curtain wall installers are placed under time

pressure.

For the thermal movement in different material, it is expected to be more serious in super

high rise buildings. For most of the daytime, the sun directly shone onto the curtain wall

without any shading from other buildings. Therefore, the temperature of the components

could be very high. Expansions of materials thus are great. High temperature of

components also means the temperature difference encountered by the curtain wall is

great.

7.3.1.3 Factors Worsening effect of Defects

Other than the 3 highly ranked factors as discussed above, there is another highly ranked

factor as shown in Table 7.6. It is “(Design) Ignoring Maintenance requirements in the

design”. This is regarded as factors worsening effect of defects by the Maintenance

Officer. According to the Maintenance Officer, the loading capacity of gondola that used

in glass replacement is inadequate. Problems arise when a relatively large piece of glass

panel required to be replaced. After putting the huge glass onto the gondola, the gondola

can only carry 1 to 2 persons. Compared with large loading capacity gondolas in other

curtain wall buildings (able to carry 3 to 4 persons after huge glass is put), the

Maintenance Officer expresses that longer time is required for large glass’s replacement

works. He suggests the designer should have considered this in the curtain wall design.

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7.3.2 Building no.2


Building no.2 is a high-rise office buildings located near Tai Kok Tsui seafront. It is

about 30 storeys. All four sides of building are enclosed by curtain wall, and the age of

this building is about 5 years. As Seeley (1987) mentioned, in fairly early life of the

building, rectification works arises from shortcomings in design, inherent faults in or

unsuitability of components, damage of goods in transit or installation and incorrect

assembly are done. Because the age of the building is only about 5 years, it is expected

that by studying the rectification works of the building, the faults in design or

construction could be known. Table 7.1 shows its curtain wall design as well as the

general situation of curtain wall defects in the building.


Type of Joint Filled Joint


Materials Tempered glass, Single glazing

Aluminum fixings


Sealant failure (no. /yr) 0.000



0.800 (location: roof)

Repair cost of


1 : 0 (under developer’s DLP) : 1



0.3% (sealant repairing not included)

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Other Defects (no.) Fixing:

- Looseness: 1

- Missing parts: 1

Maintenance Corrective planned maintenance


of Building no.2

In Table 7.2, there are three things to be noted. The first thing is the glass breakage. From

the Table 7.2, there is approximately 1 glass broken in each year. As the building have

only been operated for about 5 years, the deterioration of materials (e.g. glass, sealant and

fixings) should not be great. Therefore, there should be some special reasons for this

defect item. The second thing need to be noted is that water seepage occurs in the curtain

wall in a new building. Although compared to other buildings, water seepage is not very

serious, reasons behind the formation of this defect should also be noticed. The last thing

need to be noted is the looseness and missing parts in the curtain wall fixings. For the

reason of missing parts in fixings, the Maintenance Officer addressed that it could not be

identified. With similar reason to that of glass breakage and water seepage, reasons

behind the formation of this defect should also be noticed.

For the curtain wall maintenance of Building no.2, it is identified as corrective planned

maintenance. Although the whole curtain wall system will not be checked regularly by

specialists, certain things are planned in its maintenance. Similar to that of Building no.1,

spare packages of glass panels are stored. Furthermore, procedures for tackling defects

upon their occurrences are planned. With this emergency maintenance and spare

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resources prepared for defect rectification, it is appropriate to identify Building no.2’s

curtain wall maintenance as corrective planned maintenance.


As shown in Table 7.6, the highest ranks in defects’ cause marked by the Maintenance

Officer of Building no.2 is only “(Others) Accidental Damage”. According to the

Maintenance Officer, the accidental damage is mainly birds hitting and breaking glass

panels. This is ascertained by birds’ remains found in the podium. All of the 6 records of

glass breakage could be attributed to this cause. This explains why glass breakage records

are present in such a new building.

Although in the Case Study Questionnaire, the Maintenance Officer could only identify

one major cause of curtain wall defect, he identified another major cause while answering

the open-end question about causes of defects. It is the inadequate control in installers’

workmanship. This cause could be justified with the general situation of curtain wall

defects. As mentioned, defects are found in curtain wall sealants in such a new building.

Together with the loosening and missing parts of fixing, it could be determined that

workmanship is not good in particular parts of curtain wall. However, as within 5 years,

the water seepage is not very serious while there is only 1 record for each of the fixings’

defects, the general workmanship of the building is good. This should be the reason why

the Management Officer marking the defects’ cause “poor site assembly” as “does not

effect” the occurrences of the defects.

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Other than “(Others) Accidental Damage” being highly ranked, there are two other

factors which are also highly ranked (as shown in Table 7.6). They are “(Management)

Lack of asset register providing components, materials and system making up curtain

wall system” and “(Management) Lack of as-built drawings”. They are regarded as

factors worsening effect of defects by the Maintenance Officer. The Maintenance Officer

expresses that the curtain wall designer did not leave enough information of the curtain

wall system for their reference. When defects occur and details and drawings of the

curtain wall are requested by the remedial contractors, Maintenance Officer could not

provide these details or drawings. Remedial works are done without referencing to the

design of curtain wall. Therefore, it is less convenient for the remedial contractors to

repair curtain wall defects.

7.3.3 Building no.3


Building no.3 is a high-rise office buildings located in Mongkok. Its number of storey is

“20-29”, while the age of this building is “20-30 years”. All four sides of building are

enclosed by curtain wall. The building is divided in two parts. The first part is G/F to 3/F,

where it is in 100% site coverage and enclosed by curtain wall. The second part is the

floors above the podium on 4/G, which is also enclosed by curtain wall. Table 7.3 shows

its curtain wall design as well as the general situation of curtain wall defects in the

building.

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Materials Tempered glass, Single glazing, Aluminum fixings





1.000

Repair cost of


10:13:0



1%

Other Defects Aluminum panel:

Staining (30%)

Corrosion (30%)

Maintenance Corrective maintenance


of Building no.3

In Table 7.3, it should be noted that in every year, 2 glass breakages, 30% staining /

corrosion of aluminum panels are recorded. This is quite serious compared with other

buildings. Reason of this is explained in 7.3.3.2.

For the curtain wall maintenance of Building no.3, it is identified as corrective

maintenance. According to the Maintenance Officer, only procedures for tackling curtain

wall defects upon their occurrences are planned. This is a kind of emergency maintenance.

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Therefore, maintenance method of Building no.3’s curtain wall is classified as corrective

maintenance.


As shown in Table 7.6, there is no particularly highly ranked in defects’ causes marked

by the Maintenance Officer of Building no.3. It is explained by the Maintenance Officer

being a building aged 23, together with the fact that its curtain wall is well-designed and

constructed, the cause of its curtain wall defects is mainly natural deterioration of

materials. Relatively high age of the building explains why breakages of glass panels and

staining / corrosion of aluminum panels are relatively high in Building no.3.


Although there is no particularly highly ranked in defects’ causes that is regarded as

major defects’ causes, there are two factors being highly ranked (as shown in Table 7.6).

They are “(Design) Ignoring access for maintenance equipment” and “(Maintenance)

Long response time” According to the Maintenance Officer, as 1 of the 4 sides of curtain

wall is too close to an adjacent building (as shown in Photo 7.1), maintenance work is

quite difficult for that side of curtain wall. The gondola has to be operated very carefully

in order not to damage the curtain wall of Building no. 3 or the envelope of the adjacent

building.

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Photo 7.1 Photo showing 1 Side of Curtain Wall being too close to an Adjacent Building

For the high ranking of “Long response time”, the Maintenance Officer explained that is

mainly due to safety requirements. In replacing components of the building, application

for statutory approval and document preparation (e.g. labour insurance) are required. In

addition, located in a busy street in Mongkok, time for work commencement is very

limited. All of these make maintenance of curtain wall more difficult.

7.3.4 Building no.4


Building no.4 is another high-rise office buildings located in Mongkok. Its number of

storey is “30-39”, while the age of this building is “5-10 years”. All four sides of building

are enclosed by curtain wall. Table 7.4 shows its curtain wall design as well as the general

situation of curtain wall defects in the building.

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[gaskets joint for scuttles]

Type of glass fixing Adaptor


Glass Breakage (no. /yr) 0.100 (The only 1 breakage is in York)



associated with sealant failure) 40.000

Repair cost of


Unknown

(not yet over 10-year DLP while other defects are rare)



Unknown

(not yet over 10-year DLP while other defects are rare)

Other Defects Nil

Maintenance Corrective maintenance


of Building no.4

In Table 7.4, it should be noted that although there are only 1 record of glass breakage in

the building, both sealant failure and water seepage are quite serious. According to the

Maintenance Officer, in the 40 water seepage records per year, most of them are from the

panel, while less water seepages are found in scuttles overhead. These seepages appears

during heavy rains. However, as adaptors is used in the curtain wall design (i.e. adaptors

are glazed to the glass panel in factories and shipped to site), a better quality of sealant

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application should have been given (when compared to glazing beads) (Zhou, 2002). The

result is greatly different from what is expected.

For the curtain wall maintenance of Building no.4, it is identified as corrective

maintenance. It is because similar to that of Building no.3, only procedures for tackling

curtain wall defects upon their occurrences are planned. The Maintenance Officer also

admits that defects identification is quite heavily rely on cleaning contractors.



Officer of Building no.4 are “(Design) Inadquate communication between designer and

other key project parties (including BM)”, “(Design) Ignoring aggressive

environmental effects” and “(Maintenance) Non-compliance with specified cleaning

method”. The Maintenance Officer strongly believes that if communication is possible

between the curtain wall designer and him, the seriousness of defects in the building

could have been decreased.

For the “(Design) Ignoring aggressive environmental effects”, Maintenance Officer

expresses that the environment of the building is quite aggressive. It is because in 3 of the

4 sides of the building, there are no buildings higher than 5 storeys. Strong winds can be

directly blown onto the curtain wall. The Maintenance Officer thinks that this is the major

cause of water seepage as with such strong winds directly blown onto the curtain wall,

rain water is strongly forced to enter the curtain wall through curtain wall’s weak points.

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Another defects’ cause concerned by the Maintenance Officer is that curtain wall is being

damaged during the cleaning. Because there is no specified detergents requested by the

designer in curtain wall cleaning, whether the detergent used is harmful to the sealant is

not known by the Maintenance Officer. In addition, as it is impossible for management

staff closely supervising the curtain wall cleaning process, whether the sealant is being

damaged by workers using too great strength in cleaning areas around the sealant is also

unknown.

On the other hand, when the curtain wall is observed by the author with the Maintenance

Officer, it is found that in the connections of glass panels and transoms, only the outer

face (directly contact with outdoor environment) is applied with sealants. The inner face

of the connections is not applied with sealants (as shown in Photo 7.2). This construction

fault is suspected to be the major cause of water seepage in the building.

Outdoor

Indoor

Photo 7.2 Photo showing only the Outer Face of the Connection is Applied with Sealants

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As the defect liability period from the developer is soon expired, the Maintenance Officer

has obtained drawings of the curtain system in recent. According to the Maintenance

Officer, the cost of obtaining such drawings (about 40 drawings in total) is quite costly in

the past. The Buildings Department charged about $700 for each copy of drawings.

However, in these 2-3 years, price of each copy of drawings is it is much cheaper (about $

50 each). This may be the reason why in the past, once curtain wall drawings are lost,

most Maintenance Officers are less motivated to purchase these drawings from the

Buildings Department. As mentioned in the case study of Building no.2, lack of

information on curtain wall system may have adverse effect on the curtain wall remedial

works.

7.3.5 Building no.5


Building no.5 is a high-rise office buildings located in Kwai Hing. Located in Kwai Hing,

the building is surrounded by various industrial buildings. Its number of storey is “30-39”,

while the age of this building is “5-10 years”. Only 1 side of building is enclosed by

curtain wall. Table 7.5 shows its curtain wall design as well as the general situation of

curtain wall defects in the building.

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Type of Joint Filled Joint [Metal panels]

+ Gasket joint [Glass panels]

Type of glass fixing Adaptor



Sealant failure (no. /yr) 0.000 (type: softening and normal weathering)


associated with sealant failure) 1.000

Repair cost of

glass breakage : sealant : fixing Unknown


defects on total maintenance cost Unknown

Other Defects Nil

Maintenance - Scheduled maintenance

- Corrective planned maintenance


of Building no.5

In Table 7.5, few defects appear in this building. Note that although the Building

Manager indicates that there is no sealant failure reported in the building, the author

discovers some in the site visit. However, the identified sealant failure seems not affect

the performance of curtain wall. This maybe the reason why these sealant failure are not

reported.

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For the curtain wall maintenance of Building no.5, it is identified as scheduled

maintenance plus corrective planned maintenance. It is because similar to that of Building

no.1, regular inspections (visual inspection by the maintenance staff in every 4 months),

emergency procedures for curtain, as well as storage of spare parts (1-2 pieces for each

type of panels) are present in the maintenance. Although for regular inspections, it is less

formal than that of Building no. 1, it is also determined as an activity for scheduled

maintenance.

7.3.5.2 Major Defects’ cause of Building no.5


Officer of Building no.5 are “(Others) Wind debris”, “(Design) Ignoring aggressive

environmental effects” and “(Design) Thermal movement in different material”. For

wind debris damaging the curtain wall, according to the Maintenance Officer, it is mainly

wood logs from surroundings. It is expected that these wood debris left by the logistics

workers on the floor are common in industrial areas. Therefore, the Maintenance Officer

proposed that debris in industrial areas make the sites’ environment quite aggressive for

curtain wall. Therefore, together with the higher level of pollutant in industrial area,

“Ignoring aggressive environmental effects” is also ranked highly by the Maintenance

Officer. In the view of the Maintenance Officer, the temperature difference in Hong Kong

is quite large. Because of this, “Thermal movement in different material” is highly

ranked by the officer. Ease of sealant failures is expected to be resulted.

On the other hand, while the author observed closely to the curtain wall it is discovered

the joint failure is quite serious. As shown in Photo 7.3, the vertical sealant located in the

bottom part of the photo is totally missing. For the horizontal sealant, some areas of it is

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also missing. It is suspected to be caused by hardening of sealant by air pollutants then

the squeezing force of thermal movement in different material. Rusting of screws (also

shown in the Photo 7.3) by air pollutants also push the sealant away from the joint.

Photo 7.3 Sealant Failure of the Building no.5

Other than these major defect causes, another defect cause is revealed by the Maintenance

Officer in answering the open-ended question. It is occupants forget to close the

operatable curtain wall panels during typhoon. During the site visit, the author observed

more than 10 curtain wall panels are open (an example is as shown in Photo 7.4).

According to the Maintenance Officer, although occupants are encouraged not to open the

panels for safety reasons, many occupants choose to open the panels. It is because they

would like to have fresh air inlets. Opening panels are more common after the SARS in

2001. Compared with the operatable scuttles in Building no.4 (as shown in Photo 7.5), the

design of operatable parts of curtain wall in Building no.5 have much higher potential to

be damaged. Therefore, design of curtain wall system may also affect the occurrences of

curtain wall defects.

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Photo 7.4 An example Glass Panels being Opened Widely

Photo 7.5 Design of Operatable Part (Scuttle) of Curtain Wall in Building no.4


In identifying the cause worsening the effect of defect, the Maintenance Officer ranked

“(Design) Ignoring access for maintenance equipment” highly. The Maintenance Officer

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explains that 30% of curtain wall panels are inaccessible by gondola. Therefore, it is more

difficult for defect remedial works carried out in such areas of the curtain wall.

Similar to Building no.2, “(Management) Lack of asset register” and “(Management)

Lack of as-built drawings” are ranked highly by the Maintenance Officer. Therefore, this

lack of information makes remedial contractors less convenient in repairing curtain wall

defects.

Building no. Causes of curtain walling defects 1 2 3 4 5

I. Design Civil design Inadequate provisions for movement 2 1 1 - 1 Ignoring aggressive environmental effects 3 1 1 3 3 Ignoring biological effects 1 1 1 1 1 Inadequate structural design 1 1 1 - 1 Ignoring load impact on structural stability 1 1 1 - - Exceeding allowable deflection limits 2 1 - 1 1 Ignoring wind effects on the structure 2 1 - 1 2 Architectural design Specifying incompatible exterior finishes with the climate 2 1 1 1 -

Ignoring climatic effects on exterior shapes 3 1 1 1 1 Designing inadequate joints between finished surfaces 2 - 1 - 1

Architects’ insufficient access to basic data such as British Standard 1 - - - -

High complexity of curtain walling system design 3 1 1 1 1

Inadquate communication between designer and other key project parties (including BM) 2 1 - 4 1

Maintenance practicality and adequacy Ignoring access for maintenance equipment 2 1 3 1 3 Designing permanent fixations 2 3 1 1 1 Ignoring maintenance equipment availability 2 1 1 1 1 Ignoring maintenance requirements in the design 5 1 1 1 1

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Construction materials Thermal movement in different material 4 1 1 1 3 Selection of materials unsuitable for climatic conditions 3 1 1 1 1

Use of non-durable materials 2 1 1 1 2 Consultant firm administration and staff - - - - - Construction specifications - - - - - Construction drawings - - - - -

II. Construction Construction inspection - - - - - Civil Construction - - - - - Contractor administration Non-compliance with specifications - 1 1 - - Large and complex construction project on tight completion deadline 4 - - - -

Hiring unqualified workforce - - 1 1 - Inability to read drawings - - - - - Insufficient site inspection - - - - - Poor communication between the owner and architect/ engineer - - - - -

Hiring unqualified supervisors - - - - - Multinational construction experience - - - - - Workforce’s practice and performance Poor site assembly of the system 2 1 1 1 - Use of expired materials 2 - - - - Poor material handling and storage 2 - 1 - - Construction equipment - - - - - Construction drawings - - - - -

III. Maintenance Maintenance practices Non-compliance to specified cleaning methods and equipment 1 1 1 2 2

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Inadequate frequency of maintenance 1 1 1 1 2 Budget constrain of maintenance expense 1 1 1 1 2 Maintenance competency Maintenance staff lack of relevant experience 1 1 1 1 2 Inadequate quality of supervision 2 1 1 1 2 Inadequate qualify of maintenance manuals 2 1 1 1 1 Remedial contractors competency Inadequate quality of remedial work 1 1 1 1 2 Long responses time 1 1 2 1 1 Long restoration and repair time 1 2 1 1 1 Inadequate standard of workers’ skill set, qualification and experience 1 1 1 1 2

Information Problem Lack of asset register providing components, materials and system making up curtain walling system

2 3 1 1 1

Lack of as-built drawings 1 3 1 1 2

IV. Other Causes Damage my human Deliberate damage 1 1 1 2 4 Accidental damage 1 5 1 1 4 Damage by wind debris 5 1 1 - 2

Table 7.6 Ranking of Factors affecting the Occurrence of Defects/ Effect of Defects by

Respondents of Buildings Studied

7.3.6 Company A - Curtain Wall Consultant

7.3.6.1 General Information of the Company and the Respondent

Company A is a specialist consultancy company in curtain wall industry who provides the

following services:

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• Professional Curtain Wall Consultancy to Architects, Main Contractors and

Developers

• Performance Tests for Curtain Walls, Aluminum Windows, Glass walls and

Skylights etc

• Structural Calculations for Curtain Walls, Windows, Stone Claddings and other

Building Facade Systems

• Various Tests on Building Materials

• T4 Site Safety Supervisions

• Professional Inspection on Building Facade Failures

• Estimation of Design Wind Pressures for Building Facade Systems with Hong

Kong, or other national Wind Codes or with Wind Tunnel Tests

The respondent, Dr. Zhou is the Director of the Company A. Dr. Zhou became involved

in the curtain wall industry in 1995 when he joined a curtain wall manufacturer. His

responsibilities include: structural calculations of curtain wall systems and management

of curtain wall projects. Dr. Zhou joined a leading curtain wall testing company in Hong

Kong in early 1997 where he had the opportunity to see a lot of different curtain wall

designs from the testing mock-ups which were built for performance tests based on their

typical designs. The failures of the curtain wall systems during the tests whenever

happens were analyzed, and remedial works were witnessed and recorded in testing

reports. During his stay as a senior engineer in this testing company, he has conducted

performance tests for more than 350 projects on different building cladding systems.

Tests were conducted to various international standards including ASTM, BS, AS/NZS

and PR China's GB/T. Dr. Zhou has inspected on cladding failures to various buildings

and provided remedial proposals. He has also helped cladding contractors to determine

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the wind pressures on buildings of different shapes and at different locations by using

wind tunnel tests and/or the Hong Kong wind code. (Source: Company A’s website)

7.3.6.2 Major Defects’ cause Identified

As shown in Table 7.7, many of the defect causes are ranked 4 or above. In various

design faults, “(Design) Thermal movement in different material” and “(Design) Lack of

references” are ranked to have “strongly effect” on the curtain wall defect. In the answer

of open-ended questions, Dr. Zhou expresses that expansion joints in the curtain wall are

usually not having enough flexibility. Together, with high thermal movement in different

material, damages of components (e.g. sealants) are resulted. Lack of references in

construction design drawings increases the chance of curtain wall not being assembled as

what the designers thought.

For the construction aspect, in the open-end question, Dr. Zhou answered that curtain wall

defects are mainly caused by poor workmanship. In Table 7.7, “(Construction) Lack of

inspection”, “(Construction) Hiring unqualified inspectors” and “(Construction) Large

and complex construction project on tight completion deadline” are ranked as 5. These

are the major reasons that poor workmanship is resulted in certain curtain wall projects

curtain wall. On the other hand, for the maintenance part of curtain wall, only

“(Maintenance) Budget constrain of maintenance expense” is ranked as high as 5.

Other causes are pointed out by Dr. Zhou in the open-ended question asked. They are

aging of materials and careless in cleaning during maintenance period.

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7.3.7 Company B - Curtain Wall Design, Supply and install Company

7.3.7.1 General Information of the Company

Company B is a Company which design, supply and install curtain wall. In addition, it

provides contractors with full engineering services, as well as offering them with different

proprietary products and services. In looking at its job reference, it is found that the

company mainly focused on metal & steel work of curtain wall. (Source: Company B’s

website)

The respondent, Mr. Leung, is the Managing Director of Company B.


As shown in Table 7.7, many of the defect causes are ranked 3 (moderately effect) or 4

(highly effect). For defects’ causes ranked as 4, they only appear in design and

construction aspects. Defects’ causes ranked as 4 in design aspect include causes in sub-

groups “Civil design”, “Architectural design”, and “Consultant firm administration and

staff”. For construction faults, individual cause item “(Construction) Non-compliance

with specifications” and “(Construction) Hiring unqualified workforce”, as well as

causes in group “Workforce’s practice and performance” are ranked as 4.

7.3.8 Company C - Curtain Wall Design, Engineering and Construction Company

7.3.8.1 General Information of the Company

Company C is a company specializes in design and creation of facades. It is an

international company that facades in The Center in Hong Kong, the Changi Glass

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Atriums at Singapore Airport, Rialto, Nauru House, Eureka Tower in Melbourne, Silver

tower in Beijing and Citic Square in Shanghai are designed and constructed by the

company. Therefore, it has great experience in the design, engineering and construction

of curtain wall systems. Over the past 10 years they have been involved in over 3000

floors of curtain wall construction. (Source: Company C’s website)

The respondent, Mr. Wong, is a Senior staff of Company C.


As shown in Table 7.7, for defects’ causes ranked as 4 (highly effect), they only appear in

design and construction and “other” aspects. In design aspect, individual defects’ cause

items “(Design) Inadequate structural design” and “(Design) Ignoring wind effects on

the structure”, as well as items in sub-group “Consultant firm administration and staff”

are ranked as “highly effect” by the respondent. On the other hand, “(Construction) Non-

compliance with specifications” and “(Construction) Wrong use of equipment” are

highly ranked. In “Other Causes” aspect, “(Other) Damage by wind debris” is also ranked

as 4.

In the phone interview, moreover, Mr. Wong adds that for the stick system, curtain wall

defects mainly caused by the installation fault, or by accident. As a contactor of a number

of projects, he commends that poor sealant application is the major cause of sealant

failure. It is because during sealant application, it is not possible to have a supervisor to

supervise the work process. Therefore, the quality of workmanship is not supervised but

checked only after the curtain wall has been built. This is done by having site water tests,

having site pull-out tests, checking printing documents from supplier and having visual

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inspection checking whether primer is added. For the defect caused by accident, it is

mainly for glass breakage.

Causes of curtain wall defects Company A (Curtain Wall Consultant)

Company B (Curtain Wall

Design, Supply and install Company)

Company C (Curtain Wall

design, engineering and

construction Company)

I. Design Civil design Inadequate provisions for movement 4 4 3 Ignoring aggressive environmental effects 3 4 2 Ignoring biological effects 2 3 2 Inadequate structural design 2 4 5 Ignoring load impact on structural stability 1 4 5 Exceeding allowable deflection limits 1 4 4 Ignoring wind effects on the structure 1 4 5 Architectural design Specifying incompatible exterior finishes with the climate 4 4 4 Ignoring climatic effects on exterior shapes 4 4 4 Designing inadequate joints between finished surfaces 4 4 3

Architects’ insufficient access to basic data such as British Standard 4 3 2

High complexity of curtain walling system design 4 3 4

Inadequate communication between designer and other key project parties (including BM) 2 3 4

Maintenance practicality and adequacy Ignoring access for maintenance equipment 3 3 3 Designing permanent fixations 3 3 3 Ignoring maintenance equipment availability 3 3 3 Ignoring maintenance requirements in the design 4 3 3

Construction materials Thermal movement in different material 5 3 4

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Selection of materials unsuitable for climatic conditions 4 3 4

Use of non-durable materials 2 4 4 Consultant firm administration and staff Lack of QA/QC programme during design 3 4 2 Insufficient technical updating or staff training 4 3 4

Hiring unqualified designers 4 4 5 Lack of designer field experience 4 4 5 Lack of designer’s technical background 4 4 5 Designer ignorance of material performance 4 4 5 Misjudgement of climatic conditions 3 4 5 Construction specifications Unclear specifications 4 3 4 Inadequate definition of material type 4 3 4 Overlooking QA/QC construction procedures 2 3 3 Specifying inadequate mix design 4 3 3 Construction drawings Lack of references 5 3 3 Conflicting details 3 3 3 Lack of details 3 3 3

II. Construction Construction inspection Lack of inspection 5 3 4 Hiring unqualified inspectors 5 3 4 Neglect of the importance of inspection 4 3 4 Not implementing corrective actions during job execution 2 3 4

Civil Construction Inadequate measurements 3 3 4 Lack of communication 3 3 4 Contractor administration Non-compliance with specifications 4 4 5 Large and complex construction project on tight completion deadline 5 3 4

Hiring unqualified workforce 3 4 5 Inability to read drawings 4 3 5 Insufficient site inspection 3 3 4

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Poor communication between the owner and architect/ engineer 2 3 4

Hiring unqualified supervisors 3 3 4 Multinational construction experience 2 3 2 Workforce’s practice and performance Poor site assembly of the system 4 4 4 Use of expired materials 2 4 3 Poor material handling and storage 3 4 3 Construction equipment Wrong use of equipment 3 3 5 Inadequate performance of equipment 3 3 4 Lack of required amount of equipment 3 3 4 Construction drawings Lack of references 5 3 3 Conflicting details 3 3 2 Lack of details 3 3 3

III. Maintenance Maintenance practices Non-compliance to specified cleaning methods and equipment 3 3 2 Inadequate frequency of maintenance 4 3 2 Budget constrain of maintenance expense 5 3 2 Maintenance competency Maintenance staff lack of relevant experience 4 3 2 Inadequate quality of supervision 4 3 2 Inadequate qualify of maintenance manuals 3 3 2 Remedial contractors competency Inadequate quality of remedial work 4 3 3 Long responses time 2 3 3 Long restoration and repair time 2 3 3 Inadequate standard of workers’ skill set, qualification and experience 3 3 3

Information Problem Lack of asset register providing components, materials and system making up curtain wall system

3 3 2

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Lack of as-built drawings 4 3 1 IV. Other Causes

Damage my human Deliberate damage 1 3 2 Accidental damage 4 3 2 Damage by wind debris 4 3 4

Table 7.7 Ranking of Factors affecting the Occurrence of Defects/ Effect of Defects by

Respondents of Companies Interviewed

7.4 General Discussion of Case Study Questionnaire Results

7.4.1 Cases of Building

A summery of general information of the curtain wall defects in the buildings studied is

as shown in the Table 7.8. As all of the cases studied are stick system, the affect of type

of curtain wall on defect occurrences could not be investigated. Furthermore, the numbers

of defect vary differently from buildings with different kinds of joint or differents kind of

glass fixing (glazing beads / adaptors). Although it is proposed in the literature that

curtain walls using adaptors have fewer chances to have water seepage, no conclusion of

whether these 2 factors affecting the defect occurrences can be drawn.

In looking the number of defects, Table 7.8 shows that in general, sealant failure and

water seepage occurs more frequently than that of glass breakage. However, the ratio of

repair cost of glass breakage to sealant nearly 1:1. On the other hand, the percentage of

management cost spending on the curtain wall defects is only below 1%. This shows that

if seriousness of a defect is determined by the amount of money spend on it, seriousness

of sealant failure and water seepage is equal to that of glass breakage, while the altogether

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curtain wall defects are generally not serious compared to other items in building

maintenance (e.g. security, remedial works for E&M services).

Building no. 1 2 3 4 5 Type of curtain wall Stick System Stick System Stick System Stick System Stick System

Type of Joint Drainage Joint Filled Joint Filled Joint

Filled Joint [gaskets in

scuttle]

Filled Joint [Metal panels]

+ Gasket joint [Glass

panels Type of glass fixing Glazing Bead Glazing Bead Glazing Bead Adaptor Adaptor

Glass Breakage (no. /yr)

0.500 (610 at 1999) 1.200 2.000

0.100 (The only 1

breakage - in York)

1.500

Sealant failure (no. /yr) 38.461 0.000 2.000 40.00 0.000

Water Seepage (no. /yr) 38.461 0.800 1.000 40.00 1.000

Repair cost of glass breakage : sealant : fixing

1:1:0 1 : 0 (under developer’s

DLP) : 1 10:13:0

Unknown (just over DLP and

other defects are rare)

Unknown

% of total repair cost in curtain wall defects on total maintenance cost

<1% (3% if York’s damage

included)

0.3% (sealant repairing not

included) 1%

Unknown (just over DLP and

other defects are rare)

Unknown

Other Defects

Staining /yr 0.160

Vacuum layer failure/yr

3.077

Fixing /yr: Looseness: 1

Missing parts: 1

Aluminum panel (area):

Staining (30%)

Corrosion (30%)

Nil Nil

Table 7.8 Defects’ information of Building no. 1 to no. 5

The mean score average of the sub-groups in different buildings are shown in Table 7.9.

Indicated by different font types and sizes, it is known that curtain wall defects in

buildings studied is mainly caused by “Other Causes”, either by wind debris, birds hitting

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and deliberate damage. For defect causes in construction aspect, they are usually not

ranked by Maintenance Officers (indicated by “ - ” in Table 7.9). It is because all of them

did not participate in the curtain wall construction. However, in studying the defects in

new buildings studied, construction faults can be identified.

Another finding is that the design for curtain wall is not common to be regarded as a

major source of curtain wall defects’ causes. Instead, it is regarded as factors worsening

the adverse effects of defects, mainly by introducing inconveniences to and increasing

time for remedial works.

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Mean Score Building no. Sub-group of causes of curtain walling

defects 1 2 3 4 5

I. Design Civil design 1.71 1.00 1.00 1.50 1.50 Architectural design 2.17 1.00 1.00 1.75 1.00 Maintenance practicality and adequacy 2.75 1.50 1.50 1.00 1.50 Construction materials 3.00 1.00 1.00 1.00 2.00 Consultant firm administration and staff - - - - - Construction specifications - - - - - Construction drawings - - - - -

Group Average 2.41 1.13 1.12 1.38 1.50 II. Construction

Construction inspection - - - - - Civil Construction - - - - - Contractor administration 4.00 1.00 1.00 1.00 - Workforce’s practice and performance 2.00 1.00 1.00 1.00 - Construction equipment - - - - - Construction drawings - - - - -

Group Average 3.00 1.00 1.00 1.00 - III. Maintenance

Maintenance practices 1.00 1.00 1.00 1.33 2.00 Maintenance competency 1.67 1.00 1.00 1.00 1.67 Remedial contractors competency 1.00 1.25 1.25 1.00 1.50 Information Problem 1.50 3.00 1.00 1.00 1.50

Group Average 1.29 1.56 1.06 1.08 1.67 IV. Other Causes

Damage my human 1.00 3.00 1.00 1.50 4.00 Damage by wind debris 5.00 1.00 1.00 - 2.00

Group Average 3.00 2.00 1.00 1.50 3.00 Table 7.9 Mean Score in the Ranking of Factors affecting the Occurrence of

Defects/ Effect of Defects

7.4.2 Consultant / Design Company

The mean score average of the sub-groups in different buildings are shown in Table 7.10.

As shown in Table 7.10, the group average score of design, construction, maintenance

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and other causes are quite even. However, in several items, high rankings from 3

companies agreed with each other. They are listed as follows;

Design:

- Architectural design, Construction materials, Consultant firm administration and

staff, Construction specifications

Construction:

- Construction inspection, Contractor administration

Other Causes:

- Damage by wind debris

As mentioned, because most Maintenance Officers do not participate in the curtain wall

construction, the major causes of defect related to construction faults could only be

identified them. The “Construction” part findings in Table 7.10, as well as findings from

phone interviews, could act as supplements to the case studies of buildings. They show

that in construction aspect, poor construction inspection and poor contractor

administration causes curtain wall defects. Moreover, according to Mr. Wong, these

construction faults in sealant application greatly increase the chance for water seepage

occurrences.

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Sub-group of causes of curtain wall defects

Company A (Curtain Wall Consultant)

Company B (Curtain Wall

Design, Supply and install Company)

Company C (Curtain Wall

design, engineering and construction

Company)

I. Design Civil design 2.00 3.86 3.71 Architectural design 3.67 3.50 3.50 Maintenance practicality and adequacy 3.25 3.00 3.00 Construction materials 3.67 3.33 4.00 Consultant firm administration and staff 3.71 3.86 4.43

Construction specifications 3.50 3.00 3.50 Construction drawings 3.67 3.00 3.00 Group Average 3.35 3.36 3.59

II. Construction Construction inspection 4.00 3.00 4.00 Civil Construction 3.00 3.00 4.00 Contractor administration 3.25 3.25 4.13 Workforce’s practice and performance 3.00 4.00 3.33 Construction equipment 3.00 3.00 4.33 Construction drawings 3.67 3.00 2.67 Group Average 3.32 3.21 3.74

III. Maintenance Maintenance practices 4.00 3.00 2.00 Maintenance competency 3.67 3.00 2.00 Remedial contractors competency 2.75 3.00 3.00 Information Problem 3.50 3.00 1.50 Group Average 3.48 3.00 2.13

IV. Other Causes Damage my human 2.50 3.00 2.00 Damage by wind debris 4.00 3.00 4.00 Group Average 3.25 3.00 3.00


Defects/ Effect of Defects

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7.5 Conclusion

From the buildings studied, curtain wall defects, especially for glass breakages, are

mainly caused by “Other Causes” (e.g. wind debris, birds hitting and damage by human),

while construction faults can be identified as a factor causing sealant failure and water

seepage in studying the defects in new buildings. However, the reason why these

construction faults are caused could not be identified in the case studies. For design faults,

instead of increasing the defect occurrence in curtain wall, they could be mainly regarded

as faults that introduce inconveniences to remedial contractors in defects repairing. In

studying rankings of defects’ causes by curtain wall contractors/ consultants, the causes

of curtain wall construction fault could be identified. They are “poor construction

inspection” and “poor contractor administration” during curtain wall installation. In the

view of both Building Managers and curtain wall contractors/ consultants, maintenance

faults are generally not regarded as a major cause to curtain wall defects.

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Chapter 8 – Conclusion

Chapter 8

Conclusion

8.1 Evaluation of the Results and Findings

Three objectives are set out in this study. These objectives are listed below;

1. To find out major forms of curtain wall defects in Hong Kong high-rise office

buildings.

2. To assess the seriousness of curtain wall defects in Hong Kong high-rise office

buildings.

3. To determine the major causes of curtain wall defects and their effects on Hong

Kong high-rise office buildings

In the following, the achievement of each objective is discussed in detail.

Objective 1: To find out major forms of curtain wall defects in Hong Kong high-rise

office buildings.

Objective 1 has been addressed as noted in Chapter 4 and 5. In Chapter 4, possible

defects identified in literatures such as Chew and Silva (2004), Tee (2004) and

Buildings Department (2002) are listed out in the Survey Questionnaire. In total, there

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are 20 defects items and they are grouped to five categories, namely glass panels,

aluminum panels, fixings, sealants / joints and others. In the first part of Survey

Questionnaire, respondents are invited to indicate whether the buildings they managed

have the defect listed in the questionnaire.

In Chapter 5, the data collected from the 23 Building Managers is analyzed and

discussed. The data obtained from the questionnaire form the basis of the first part of

research study on the incidence of curtain wall defects.

Rank Defect Item Incidence

1st Water seepage 85.71%

2nd Moisture behind curtain wall 66.67%

3rd Sealants / joints failure 61.90%

4th Shattering or falling off of glass panels 60.00%

Table 8.1 Defect Items received Top Four Ranks in their Incidence

Among 20 defects items, water seepage is the most common curtain wall defect. The

number of building having water seepage is over 80% of the samples. The incidence

of water seepage is even higher than 2nd to 4th rank defects by about 20%. This

implies that being a system composed of numerous components, curtain wall has

many weak points to water seepage. The low number of sample of curtain wall with

double glazed glass panels makes the rank of item “moisture behind curtain wall”

very high. The sealants/ joints failure is ranked closely with water seepage means that

water seepage is present associated with sealant / joints failure. Falling off of glass

panels is also quite common as shown by its high rank.

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Objective 2: To assess the seriousness of curtain wall defects in Hong Kong

high-rise office buildings.

The same as Objective 1, Objective 2 has been addressed in Chapter 4 and 5. In the

same questionnaire mentioned in the achievement of Objective 1, respondents are

further invited to give further information for the assessment of the seriousness of

each defect. The data obtained from the first and second parts of the questionnaire

form the basis of the second part of the research study on the seriousness of curtain

wall defects. The overall seriousness of the defect is assessed by both quantitative and

qualitative data: number of defects’ occurrence, affected area of curtain wall,

respondents’ general impressions on defects’ seriousness and the 4 defect quantifying

factors (tendency to aggravate the defect, tendency to form other defects, impact on

performance and ease of rectification). “Top three most serious defects” are identified

because of their close and high overall mean scores (i.e. low percentage difference

from that of 1st Rank, as shown in Table 8.2) among other defect items.

Overall Rank Defect Item % difference from 1st

Rank's Total Score

1st Water seepage -

2nd Sealants / joints failure 42%

3rd Corrosion of aluminum panels due to rain 58%

4thStaining / decolouration, surface etching of

glass panels 115%

Table 8.2 Defect Items received Top Four Ranks in their Seriousness

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With similar results found in Objective 1, the most serious defects identified are water

seepage and sealants / joints failure. This further proves their high importance in

curtain wall maintenance. The association of water seepage and sealants / joints

failure is also further indicated. Corrosion of aluminum panels is also ranked highly

by its overall seriousness. Together with the high incidence of aluminum panels’

defects revealed, more non-structural defects (e.g. decolouration, corrosion) could be

founded in aluminum panels. This result has two implications. The first one is that

defects of aluminum panels are the easiest to be observed than that of glass panels and

fixings, because of the non-shiny surfaces and light colour of aluminum panels. The

second implication is that being a metal component of curtain wall, aluminum panels

are highly attacked by acid rain compared to other curtain wall components. Fixings

seem to be least harmed either because their corrosion is “hidden”, or because they

are well-hidden under glass panels in most new curtain wall designs.

In the Survey Questionnaire, two more things about curtain wall defects are found.

The first one is that most defects are rectified by specialist curtain wall contractors. It

could be reflected by the factor “Ease of rectification” being ranked highly regardless

the type, incidence or seriousness of the defects. By this result, it is known that

Building Managers would only trust specialist curtain wall contractors in rectifying

the curtain wall. In addition, the data collected in the Survey Questionnaire also

proves that structural unsafe for curtain wall in Hong Kong is not serious in general.

This implication could be seen from the relative low overall rankings of most of the

structural defect items. This shows that both curtain wall design and installation in

Hong Kong are so mature that with certain level of maintenance, having a curtain wall

as the building’s envelope could be very safe. Only defects which are non-vital are

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more likely to appear on the curtain wall. These reasons could explain why curtain

wall is widely used as envelopes of high-rise office buildings.

Objective 3: To determine the major causes of curtain wall defects and their effects

on Hong Kong high-rise office buildings

Objective 3 is addressed in Chapter 6 and 7. Items of possible defects’ causes are

selected from previous literatures [e.g. Seeley (1987), Alves (1997) and Chew, Tan

and Kang (2004)] and listed in the questionnaire. In total, there are 72 defects’ causes

and they are grouped to four categories, namely design, construction, management

and other.

In Chapter 7, 5 out of 21 respondents’ buildings have been chosen for the Case Study

part. Moreover, curtain wall consultants / contractors are asked to fill in the same

Case Study Questionnaire. Data obtained from the case study interviews as well as

questionnaires’ results collected from consultants forms the basis of the second part of

the Study on the major causes of curtain wall defects.

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Rankings Building

no.1

Building

no.2

Building

no.3

Building

no.4

Building

no.5

Company

A

Company

B

Company

C

1stOthers

* /

Construction

*Others

* Design Others Others* Maintenance

* Design* Construction

*

2nd - Maintenance Maintenance Design Maintenance Design* Construction

* Design*

3rd Design Design Construction

/ Others Maintenance Design

Construction

*

Maintenance

* / Others

* Others*

4th Maintenance Construction - Construction - Others* - Maintenance

* Result having mean score equal to or above 3.00 (“moderately effect”)

Table 8.3 Rankings Defects’ Causes by different Buildings / Company

From the buildings studied, curtain wall defects, especially for glass breakages, are

mainly caused by “Other Causes”. Therefore, within 5 buildings studied, the top rank

of defects’ causes in 4 buildings is “Others”. In these “Other Causes”, there are

mainly 2 types, namely wind debris and birds hitting. For wind debris causing curtain

wall defects, it is found in a super high-rise building (Building no. 1) and an office

building located near industrial area (Building no. 5). On the other hand, glass

breakage due to birds hitting is found in a newly constructed office (Building no. 2).

The “Other Causes” in Building no. 5 addressed by the Maintenance Officer is the

suspected carelessness in cleaning works.

Among 5 buildings, the construction is rank highly only in Building no. 1. This is

because most BMs/MOs would not like to comment on the construction quality of the

curtain wall, as they did not participate in the curtain wall installation. For Building

no.1, during the remedial works, the BM was informed by the engineer that the

serious water seepage of the building he managed is due to poor sealant application.

In Building no. 2, although the rank of “construction” is low, the BM addresses that

- 170 -


inadequate control in installers’ workmanship may be the cause of curtain wall defects.

This could be justified with the general situation of curtain wall defects in this

five-year-old building. Firstly, it can be found that water seepage appears in this new

building. Together with the loosening and missing parts of fixing, it could be

determined that workmanship is not good in particular parts of curtain wall. However,

as within 5 years, the water seepage is not very serious while there is only 1 record for

each of the fixings’ defects, the general workmanship of the building is acceptable.

Although construction faults can be identified as a factor causing water seepage in

studying the defects in these buildings, the reasons why these construction faults are

caused could not be identified through these case studies.

In order to find out the details of construction faults, rankings of defects’ causes by

curtain wall contractors/ consultants are studied. They are “poor construction

inspection” and “poor contractor administration” during curtain wall installation.

One common construction fault identified by a respondent is poor sealant application.

It is because during sealant application, it is not possible to have a supervisor to

supervise the work process. Although the quality of sealant applied is checked by

water tests after the curtain wall has been installed, the effect of poor workmanship

may not be immediately discovered. One example is that although Building no.1 has

undergone water test after its competition, inadequate thickness of sealant could be

identified by the Building Manager after 10-year DLP is over.

According to the data from both Building Managers and Companies interviewed,

maintenance faults are generally not regarded as a major cause to curtain wall defects.

It can be shown by the maintenances’ relatively low and insignificant rankings.

However, the information problem (i.e. Lack of asset register and as-built drawings) is

- 171 -


identified in 2 of the 5 buildings. It is regarded as factors increasing effect of defects

by the Maintenance Officer because higher chances of improper or untimely remedial

works would be resulted.

For the effect of design faults on curtain wall, instead of increasing the defect

occurrence in curtain wall as expected in the hypothesis, they could be mainly

regarded as faults that introduce inconveniences to remedial contractors in defects

repairing. The first example is inadequacy of gondola’s capacity in Building no. 1.

With inadequate gondola’s capacity, large glass panels are difficult to replace.

Although defects would not be directly caused by such design fault, time for remedial

works has to increase. The effect of the defects on curtain wall may increase owing to

the delay in remedial works. Other examples of design faults include

- One side of Curtain wall being too close to an adjacent building (Building no. 3);

- Ignorance of aggressive industrial neighbourhood near the building in choosing

curtain wall as its envelope (Building no. 5), and

- Design of large operatable panels increasing the chance of glass falling if it is not

closed during typhoon (Building no. 5).

These examples support the point raised by Chew and Tan (2002) that some defects

could have been solved by the presence of (or better) communication channels

between designers and other key project parties (e.g. Building Managers).

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8.1 Limitations of the Study

The limitation of the study can be identified as 3 areas, namely the limited response

rate, the limitation in information collection and the limitation of resources.

For the limited response rate, it affects both the Survey part as well as the Case Study

part of the study. In the Survey part, as questionnaire is used for data collection, an

adequate number of respondents is essential. Levin and Rubin (1991) point out that

the resulting sample size should be over 30 in order to represent a large population.

However, in the study, the effective result sample size is about 20. Therefore, the low

resulting sample size may affect the significance of the results. In the Case Study part,

the same problem is in the resulting sample size of curtain wall consultants /

contractor. On the other hand, as in the Case Study part, Building Managers invited to

participate in the case studies are the respondents of the Survey Questionnaire, the

low number of Survey Questionnaire respondent also affects the Case Study part.

Because only a few Building Managers from several buildings could be invited to

participate in the case study, the quality of case studies chosen is could not be

controlled. For instance, the buildings studied are located in very different areas so

that great variations in the buildings’ environment are resulted. The variable of

environment cannot be removed so that whether the design faults, construction faults,

maintenance faults or other faults would affect the defects’ occurrences cannot be

decided clearly by direct comparison.

For the limitation in information collection, it is encountered by the author in both of

the Survey part and Case Study part. In the Survey part, there is a question asking the

respondents to fill in the number of defects occurred in their buildings. However,

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finding such data could be a time consuming task for the respondents. The

respondents thus would either refuse to fill in the questionnaire, or just fill in the

questionnaire with their impressions. Maintenance records would not have been

carefully looked into before filling in the questionnaire. This problem is quite serious

in large scale defect items such as water seepage. Therefore, the reliability of the

result may be affected. Similar problem is faced in the Case Study part. As the

Building Managers / Maintenance Officers interviewed do not expect that they had to

disclose the buildings’ maintenance information, the effect, causes and maintenance

cost of each type of defect could not be investigated closely. Only general comments

on such issues from the respondents could be collected.

The third limitation is the resources limitation. In this study, 3 areas (design,

construction and maintenance) are required to be investigated. Together with the

limited time for the research, this research can only gives the readers a general

introduction to the reasons behind curtain wall defects. In addition, unlike the study

reviewed in the literature that numerous parties like clients, contractors, architects,

engineers, manufacturers, suppliers, testing centers and Building Managers being

face-to-face interviewed, the author could only invite the Building Managers,

contractors and consultants to participate in the study. It is due to time and cost

constraints. Furthermore, the face-to-face interview, which is more flexible than using

questionnaire and lets more complex questions to be asked, could only held in the 5

buildings studied. The data collection method for comments from curtain wall

consultants / contractor is mainly using a preset questionnaire. Therefore, with these

time and cost constraints, only an exploratory study can be done.

- 174 -


8.2 Recommendations of Further Investigation

As mentioned, because of the exploratory nature of this research, recommendations

for further investigation are given.

In order to clearly decide whether the design faults, construction faults, maintenance

faults or other faults would affect the defects’ occurrences, the variable of

environment should be removed. Therefore, case studies of buildings focused in a

particular area (e.g. Quarry Bay) should be held. After the removal of the variable of

environment, the direct comparison of curtain wall designs, construction method,

maintenance method as well as defects occurred in the buildings could be held to

determine the defects’ cause.

According to the results of this dissertation, the defects’ causes in the aspects of

“construction” and “others” are found to be the major causes of curtain wall defects.

In view of this, the author would suggest further investigations should be focused on

these two areas.

To study the effect of construction to the occurrences curtain wall defects, a number

of case studies of newly constructed buildings (within 5 years after the completion,

like Building no. 2 in this dissertation) should be held. After that, the compare and

contrast of the time for curtain wall installation, the curtain wall installation

companies employed as well as the defects across different newly built curtain wall

office buildings could be done. Through this, how the quality of construction affect

the curtain wall can be studied. To study the reasons behind the construction faults,

construction site visits of curtain wall office buildings is further suggested. Direct

- 175 -


observation to site practices and workmanship could be used in collecting qualitative

information. Face-to-face interviews with the workers, supervisors and testers could

also be held.

In studying the “other” defects’ causes such as wind debris, one method suggested by

the author would be holding a single case study of a particular curtain wall damaged

event. An example such event is the Typhoon York in 1999 (discussed briefly in

Building no.1). Building Managers, as well as the related professionals of high-rise

office buildings in the affected area should be interviewed. Through this, the effect of

particular “other” defects’ causes on curtain wall could be studied.

- 176 -

Appendix

Material for enclosure Glass Aluminum

Structural Stability

- framed support or structural sealant with glass buttresses

- special glazing system available for large glass area, usually with suspension system

- movement joint allowed around glass

- tempered glass for better strength

- generally good structural strength

- anchored to structural system of building

- avoid common situation weakening structural strength

Safety - broken glass can be dangerous - laminated glass and tempered

glass for safety - hired glass for fire rating - fire rate glass available

- secured insulation is safe

Habitability - transmit heat and light when clear, absorptive when tinted, reflective when coated with various chemicals

- reflect sound - stops certain amount of noise,

double glazing or double window is insulative

- waterproofing at joints is achieved by sealants

- insulative materials can be added for controlling heat or sound

Durability - suitable in normal use - coating and tint can be worn off

especially during construction

- durable in most cases - oxidation for materials is

possible and many resent to form a protective layer

- fainting of colouring for certain coating

Compatibility - glass can withstand contact with most material

- coating on glass can degraded through some chemicals

- cannot be placed with other material due to galvanic action

Aesthetics - reflective, - transparent or colour tinted

- anodizing gives colour to aluminum

- paint, fluorocarbon coating, powder coating and enamel coating can be applied to produce colour and pattern

- texture can be made by engraving, embossing, etching, grinding or hammering

Appendix A Performance Characterizes of Materials for Curtain Walling Source: Wong, W. S. (1998)

- 177 -

Appendix

- 178 -

Appendix B Design Wind Pressure – a table from section 4 of Code of Practice on Wind Effects in Hong Kong 2004 Source: Buildings Department (2004)

ppendix

- 179 -

Appendix C Building Maintenance Decision Diagram Source: Horner, Haram and Munns (1997)

A

Appendix

Appendix D Parameter used in Chew, et al (2004)’s Research and their Weightings Source: Chew, M.Y.L., Tan, S.S. and Kang, K.H. (2004)

- 180 -

Appendix

- 181 -

Questionnaire Brief

In recent years, there has been an increased use of curtain wall as the external walls of

high-rise office buildings. With advantages of good appearance, space saving, lightness

and rapid construction, curtain wall is very attractive to designers. However, the

consequences of curtain wall defects could be very serious. An example of serious curtain

wall defects is the shattering of curtain walls’ glass panels of several buildings in Wan

Chai by Typhoon York in 1999.

In this Study, there are 2 parts. The first part is to identify the incidences and seriousness

of defect items by using a survey. The second part is called “Case Study” part, where

causes of defects in the buildings maintained by case study participants are investigated.

Terms used in the study

“Curtain Wall” – a form of vertical building enclosure which supports no load other than

its own weight that of ancillary components and the environmental forces which act upon

it. A rectangular grid of vertical or horizontal framing with infill panels of glass or some

other lightweight panels is usually consists.

“Defect (of Curtain Wall)” – points in curtain wall where various requirements (e.g.

performance requirements, structural requirements and durability requirements) of curtain

wall are failed to be satisfied.

“High-rise Office Building” – buildings more than or equal to 20 storeys designed for

commercial/ business purposes.

Appendix

- 182 -

Survey Questionnaire: Incidences and Seriousness of Curtain Wall Defects Part 1: Type of Defects of the Curtain Wall Q1. Please fill in the table below.

Areas of concern

Types of defects

Number of times the defect has appeared

(Since the completion of the bldg. OR Record period from 19 # to

2005)

Year(s) when the defect was repaired

(e.g. “1999, 2002-04”)

OR

Frequency of such defect being

repaired (e.g.

“x2 / yr after 1991” )

Seriousness (average) of

the defect – by observation

1 = Very low, 2 = Low, 3= High, 4= Very high*

Area (average) of curtain wall

affected

1 = 0-5%, 2 = >5-10%, 3 = >10-25%, 4 = >25-50%, 5 = >50%*

Cracking 1 2 3 4 1 2 3 4 5Shattering or falling off

1 2 3 4 1 2 3 4 5

Loosening 1 2 3 4 1 2 3 4 5

Glass panels

Staining / decolouration, surface etching

1 2 3 4 1 2 3 4 5

Cracking 1 2 3 4 1 2 3 4 5Falling off 1 2 3 4 1 2 3 4 5Loosening 1 2 3 4 1 2 3 4 5Deformation 1 2 3 4 1 2 3 4 5Staining / decolouration

1 2 3 4 1 2 3 4 5Separation, delaminating

1 2 3 4 1 2 3 4 5

Aluminum panels

Erosion due to rain water, surface abrasion

1 2 3 4 1 2 3 4 5

Looseness 1 2 3 4 1 2 3 4 5Missing parts 1 2 3 4 1 2 3 4 5Corrosion 1 2 3 4 1 2 3 4 5

Fixings (e.g. embedment, mullions, glazing beads) Damaged 1 2 3 4 1 2 3 4 5

Sealants / joints missing

1 2 3 4 1 2 3 4 5Sealants / Joints

Sealants / joints failure

1 2 3 4 1 2 3 4 5

Water seepage 1 2 3 4 1 2 3 4 5Excessive air permeability / vacuum layer failure

1 2 3 4 1 2 3 4 5

Others

Moisture behind curtain wall

1 2 3 4 1 2 3 4 5

* Please cross out the appropriate answer # Please fill in the year since the period of record started

Appendix

- 183 -

Part 2: Defect quantifying factors In the following, below four factors will be used to quantify the defects; 1. Tendency to aggravate the defect (spreading defect of the same type) 2. Tendency to form another defect 3. Ease of rectification 4. Impact on the performance Q1. Please fill in the below table to indicate the seriousness of each defect by using the factors.

1. Tendency to aggravate the defect 2. Tendency to form another defect

Areas of concern

Types of defects

Likelihood of spreading the defect is; 4 = Extremely high, 3 = High, 2 = Low, 1 = Extremely Low*

Likelihood of forming other defects is; 4 = Extremely high, 3 = High, 2 = Low, 1 = Extremely Low*

Cracking 1 2 3 4 1 2 3 4 Shattering or falling off 1 2 3 4 1 2 3 4

Loosening 1 2 3 4 1 2 3 4

Glass panels


1 2 3 4 1 2 3 4

Cracking 1 2 3 4 1 2 3 4 Falling off 1 2 3 4 1 2 3 4 Loosening 1 2 3 4 1 2 3 4 Deformation 1 2 3 4 1 2 3 4 Staining / decolouration 1 2 3 4 1 2 3 4

Separation, delaminating 1 2 3 4 1 2 3 4

Aluminum panels


1 2 3 4 1 2 3 4

Looseness 1 2 3 4 1 2 3 4 Missing parts 1 2 3 4 1 2 3 4 Corrosion 1 2 3 4 1 2 3 4

Fixings(e.g. embedment, mullions, glazing beads) Damaged 1 2 3 4 1 2 3 4

Sealants / joints missing 1 2 3 4 1 2 3 4 Sealants /

Joints Sealants / joints failure 1 2 3 4 1 2 3 4

Water seepage 1 2 3 4 1 2 3 4 Excessive air permeability / vacuum layer failure

1 2 3 4 1 2 3 4

Others

Moisture behind curtain wall (i.e. inside the bldg.)

1 2 3 4 1 2 3 4

* Please cross out the appropriate answer

Appendix Q2. Please fill in the below table to indicate the seriousness of each defect by using the factors.

Part 3: Details of the Building

3. Ease of rectification 4. Impact on the performanceAreas of concern

Types of defects

Defects can be rectified by; 1 = Any contractor, 2 = At least experienced contractor,3 = Only specialist contractor*

4 = Extremely great, 3 = Great, 2 = Not so great, 1 = Little*

Cracking 1 2 3 1 2 3 4 Shattering or falling off 1 2 3 1 2 3 4

Loosening 1 2 3 1 2 3 4

Glass panels


1 2 3 1 2 3 4

Cracking 1 2 3 1 2 3 4 Falling off 1 2 3 1 2 3 4 Loosening 1 2 3 1 2 3 4 Deformation 1 2 3 1 2 3 4 Staining / decolouration 1 2 3 1 2 3 4

Separation, delaminating 1 2 3 1 2 3 4

Aluminum panels


1 2 3 1 2 3 4

Looseness 1 2 3 1 2 3 4 Missing parts 1 2 3 1 2 3 4 Corrosion 1 2 3 1 2 3 4

Fixings(e.g. embedment, mullions, glazing beads) Damaged 1 2 3 1 2 3 4

Sealants / joints missing 1 2 3 1 2 3 4 Sealants /

Joints Sealants / joints failure 1 2 3 1 2 3 4

Water seepage 1 2 3 1 2 3 4 Excessive air permeability / vacuum layer failure

1 2 3 1 2 3 4

Others

Moisture behind curtain wall (i.e. inside the bldg.)

1 2 3 1 2 3 4

District

Name of the building: ( )**

Contact person: Email: g

Number of storey of the building: *

Age of the building: years

Area of curtain wall (including both glass and metal panels) *: a. 1 side (less than 50%) b. 1 side (more than 50%) c. 2-3 sides d. All 4 sides

* Please cross out the app

THANK YOU VERY MUCH FOR YOUR COOPERATION s
- 184 - ropriate answer

Appendix

- 185 -

Case Study Questionnaire : Curtain Wall Defects All responses will remain FULLY CONFIDENTIAL. Part 1 An open-end question about causes of curtain wall defects In your opinion, what are the causes of curtain wall defects in the building that you are managing?

Part 2 Ranking possible causes of curtain defect Please rank below items in causing the curtain wall defects in the building you are managing by putting a check mark on the appropriate answers.

Causes of curtain walling defects

Least likely

presence in this

building thus

Does notaffect

Presence in this

building and

Moderately affects

Most likely

presence in this

building thus

Strongly affects

Unknown

I. Design Civil design Inadequate provisions for movement 1 2 3 4 5 Ignoring aggressive environmental effects 1 2 3 4 5 Ignoring biological effects 1 2 3 4 5 Inadequate structural design 1 2 3 4 5 Ignoring load impact on structural stability 1 2 3 4 5 Exceeding allowable deflection limits 1 2 3 4 5 Ignoring wind effects on the structure 1 2 3 4 5 Architectural design Specifying incompatible exterior finishes with the climate 1 2 3 4 5

Ignoring climatic effects on exterior shapes 1 2 3 4 5 Designing inadequate joints between finished surfaces 1 2 3 4 5

Architects’ insufficient access to basic data such as British Standard 1 2 3 4 5

High complexity of curtain walling system design 1 2 3 4 5

Poor communication between designer and other key project parties (including BM) 1 2 3 4 5

Appendix

- 186 -


Least likely

presence in this

building thus

Does notaffect

Presence in this

building and

Moderately affects

Most likely

presence in this

building thus

Strongly affects

Unknown

I. Design (Cont’d) Maintenance practicality and adequacy Ignoring access for maintenance equipment 1 2 3 4 5 Designing permanent fixations 1 2 3 4 5 Ignoring maintenance equipment availability 1 2 3 4 5 Ignoring maintenance requirements in the design 1 2 3 4 5

Construction materials Thermal movement in different material 1 2 3 4 5 Selection of materials unsuitable for climatic conditions 1 2 3 4 5

Use of non-durable materials 1 2 3 4 5 Consultant firm administration and staff Lack of QA/QC programme during design 1 2 3 4 5 Insufficient technical updating or staff training 1 2 3 4 5

Hiring unqualified designers 1 2 3 4 5 Lack of designer field experience 1 2 3 4 5 Lack of designer’s technical background 1 2 3 4 5 Designer ignorance of material performance 1 2 3 4 5 Misjudgement of climatic conditions 1 2 3 4 5 Construction specifications Unclear specifications 1 2 3 4 5 Inadequate definition of material type 1 2 3 4 5 Overlooking QA/QC construction procedures 1 2 3 4 5

Specifying inadequate mix design 1 2 3 4 5 Construction drawings Lack of references 1 2 3 4 5 Conflicting details 1 2 3 4 5 Lack of details 1 2 3 4 5

Appendix

- 187 -


Least likely

presence in this

building thus

Does notaffect

Presence in this

building and

Moderately affects

Most likely

presence in this

building thus

Strongly affects

Unknown

II. Construction Construction inspection Lack of inspection 1 2 3 4 5 Hiring unqualified inspectors 1 2 3 4 5 Neglect of the importance of inspection 1 2 3 4 5 Not implementing corrective actions during job execution 1 2 3 4 5

Civil Construction Inadequate measurements 1 2 3 4 5 Lack of communication 1 2 3 4 5 Contractor administration Non-compliance with specifications 1 2 3 4 5 Large and complex construction project on tight completion deadline 1 2 3 4 5

Hiring unqualified workforce 1 2 3 4 5 Inability to read drawings 1 2 3 4 5 Insufficient site inspection 1 2 3 4 5 Poor communication between the owner and architect/ engineer 1 2 3 4 5

Hiring unqualified supervisors 1 2 3 4 5 Multinational construction experience 1 2 3 4 5 Workforce’s practice and performance Poor site assembly of the system 1 2 3 4 5 Use of expired materials 1 2 3 4 5 Poor material handling and storage 1 2 3 4 5 Construction equipment 1 2 3 4 5 Inadequate performance of equipment 1 2 3 4 5 Lack of required amount of equipment 1 2 3 4 5 Construction drawings Lack of references 1 2 3 4 5 Conflicting details 1 2 3 4 5 Lack of details 1 2 3 4 5

Appendix


Least likely

presence in this

building thus

Does notaffect

Presence in this

building and

Moderately affects

Most likely

presence in this

building thus

Strongly affects

Unknown

III. Maintenance Maintenance practices Non-compliance to specified cleaning methods and equipment 1 2 3 4 5

Inadequate frequency of maintenance 1 2 3 4 5 Budget constrain of maintenance expense 1 2 3 4 5 Maintenance competency Maintenance staff lack of relevant experience 1 2 3 4 5

Inadequate quality of supervision 1 2 3 4 5 Inadequate qualify of maintenance manuals 1 2 3 4 5 Remedial contractors competency Inadequate quality of remedial work 1 2 3 4 5 Long responses time 1 2 3 4 5 Long restoration and repair time 1 2 3 4 5 Inadequate standard of workers’ skill set, qualification and experience 1 2 3 4 5

Information Problem Lack of asset register providing components, materials and system making up curtain walling system

1 2 3 4 5

Lack of as-built drawings 1 2 3 4 5

IV. Other Causes Damage by human (or animals) Deliberate damage 1 2 3 4 5 Accidental damage 1 2 3 4 5

Damage by wind debris 1 2 3 4 5

Is there any other curtain defects’ causes found in your building? d

If yes, please list them out here together with their rankings.

THANK YOU VERY MUCH FOR YOUR COOPERATION

- 188 -

References

References

Buildings Department (2003) Practice Note for Authorized Persons and Registered

Structural Engineers – Cladding, PNAP 59

Buildings Department (2003) Practice Note for Authorized Persons and Registered

Structural Engineers – Curtain Wall Systems, PNAP 106

Buildings Department (2004), Code of Practice in Wind Effects in Hong Kong 2004,

Hong Kong: The Government of Hong Kong Special Administrative

Region

Buildings Department (2004), Practice Note for Authorized Persons and Registered

Structural Engineers - Code of Practice in Wind Effects in Hong Kong

2004

Catherine S, and Angus S. et al (2003) Oxford Dictionary of English (2nd ed), U.K. :

Oxford University Press

Centre for Window and Cladding Technology (1992) A comparative study of the façade

industry in the UK, Europe, Japan and the USA, Bath : Centre for Window

and Cladding Technology

Centre for Window and Cladding Technology (1996) Test methods for curtain walling,

Bath : Centre for Window and Cladding Technology

- 189 -

References

Centre for Window and Cladding Technology (1996), Standard for curtain walling, Bath :

Centre for Window and Cladding Technology

Centre for Window and Cladding Technology (2000), Technical Note No. 14 – Curtain

Wall Types

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