section 10 - green roof installation details (draft-01)

2. Roof Greening Options and Applications

10.1 In ArchSD projects, the design of installation details of green roofs is usually carried out by specialist contractors. This section briefly describes the types of green roof and summarizes the installation details adopted for three completed ArchSD projects, namely:

i) Tin Shui Wai Public Library cum Indoor Recreation Centre (PWP No. 048RG)

ii) Tseung Kwan O Complex in Area 44, Tseung Kwan O (PWP No. 190SC)

iii) Wo Hop Shek Columbarium and Garden of Remembrance (PWP No. 017NB)

10.2 Types of Green Roof

10.2.1 Green roofs are classified into two types:

i) Extensive Green Roofs are characterized by their low weight, low capital cost and minimal maintenance. They are generally lightweight systems with soil depth ranging from 50mm to 150mm. Plants are watered and fertilized only until they are established and after the first year, maintenance consists of two or three visits a year for weeding of invasive tree and shrub species, mowing, safety and membrane inspections. As a general rule, minimal technical expertise or practical experience is required for installation and maintenance.

ii) Intensive Green Roofs are characterized by greater weight, higher capital costs, more plantings and higher maintenance requirements. Plants are grown and maintained in ways similar to ground level gardens, with soil depths that vary according to plant requirements, ranging from a minimum of 200mm depth for lawns to up to 2000mm depth for tree planting, with corresponding structural loading implications. Due to increased soil depth, the plant selection can be more diverse including trees and shrubs, which allows a more complete ecosystem to develop. Requirements for maintenance and watering are more demanding and ongoing than with an extensive green roof. Intensive green roofs can be found in many building structures in Hong Kong in the form of podium level gardens.

10.2.2 In both types of green roof, all basic components are placed directly on top of the finished floor surface (screeding or water-proofing), which can be either reinforced-concrete or composite steel structure.

10.2.3 The components of a green roof system are non-structural building elements. Typical green roof construction arrangement options for long span roof structures are as follows:

Structural Engineering Branch, ArchSD of 15 File Code : LCC of long span roof.docWTL/CYT/YHC

Issue No./Revision No. : 1/- Issue/Revision Date : Mar 2013

Formation of planter with drainage systems by steel sub-frames, corrugated sheets and layers of membranes (Figure 1) – the system is designed to match with site geometry and constraints. Examples of suppliers of components include Rigisystem, Zinco, etc.; or

Installation of modular systems such as plastic trays or pre-planted mats containing the growing medium onto the finished concrete surface (Photos and examples of suppliers are shown in Figure 2); or

Constructing the planters by reinforced concrete walls or recesses in floor slabs – this arrangement is more common with intensive green roofs where the soil depths are much deeper.

Figure 1: Typical Detail of Green Roof as shown on Rigisystems website



Vegetated Mat System(Examples of suppliers: Elevated Landscape Technologies, etc.)

Tray System(Examples of suppliers: LiveRoof, Greenlink, GreenGrid, GreenTech, etc.)

Sack System:(Examples of suppliers: Green Paks, etc.)

Figure 2: Modular Green Roof Systems

10.3 Application of Green Roof in Arch SD projects

10.3.1 Appendix A describes the application of green roof for three completed Arch SD projects with illustrations of their depositions and installation details

10.3.2 In the first two ArchSD projects discussed below, the green roofs are provided on the long-span roof supported by steel trusses. Extensive green roof system was adopted instead of intensive green roof. This arrangement minimized the imposed loads on the trusses to optimize structural economy against architectural requirements.

10.3.3 The last project illustrates an example of the intensive green roof system supported by conventional reinforced concrete slab and beam structures. This type of relatively short span structures is generally more appropriate for meeting the higher loading and maintenance requirements due to the increased soil depth and watering demand respectively.

10.3 Installation Details adopted for Tin Shui Wai Public Library cum Indoor Recreation Centre (TSW-IRC)

10.3.1 The green roof system for TSW-IRC is a tailor-made system that was designed

and built by the Contractor. The roof floor itself is supported by steel trusses spanning at about 35m. Steel sub-frames and roof decking are installed onto the steel trusses to build up to the required levels and pitch angles. Waterproofing is formed by a continuous, fully lapped (50mm minimum



overlap) layer of vapour barrier is laid onto the decking, with laps and edges sealed with aluminium tape. Aluminium halters (to support the green roof), insulation and the roof panel are then installed on top of the vapour barrier.

10.3.2 The green roof system, supported on a profile decking, are installed and supported by the aluminium halters. Drainage layer and soil are then placed on this decking to complete the green roof installation.

10.3.3 The green roof system comprises of the following layers (top to bottom):

Green Roof 1. Soil, Sedummix Mat and plants2. Drainage mat and filter layer3. 0.9mm thk Rigidal 32/167/1000 Aluminium Profile4. Aluminium frame (40mm deep RHS sections) at

25mm above Building Roof, supported by aluminium halters fixed to rigidal panels below by Stainless steel screws

Building Roof 5. Rigidal Zip Lok 400 Aluminium Standing seam roof.6. Insulation7. Vapour barrier8. Roof decking – Fisher TRAPEX 150/280 1.5mm thk

GMS Decking9. Steel sub-frame to build up to Roof level as required

by ArchitectLong-span Steel Truss Supporting Roof floor

General View of Green Roof at TSW-IRC Close-Up View



Figure 3: Typical Roof Section for TSW-IRC



Steel Truss

Green Roof

Building Roof

Figure 4: Typical Detail of Green Roof for TSW-IRC (Numbers denote roof components as described in Paragraph 10.3.3)



Green Roof

Building Roof

12

3

ALUMINIUM FRAME (40MM DEEP RHS SECTIONS) AT 25MM ABOVE BUILDING ROOF, SUPPORTED BY ALUMINIUM HALTERS FIXED TO RIGIDAL PANELS BELOW BY STAINLESS STEEL SCREWS

4

5

6

78

STEEL SUB-FRAME TO BUILD UP TO ROOF LEVEL AS REQUIRED BY ARCHITECT

9

10.3.4 Some photos of the installation of the green roof system are shown below:

Steel Truss, Sub-frame and Decking Vapour Barrier, Insulation and supporting clips for roof panels

Installation of roof panels (Rigidal Zip Lok 400 Aluminium Standing seam roof)

Interlocking of roof panels panels (Rigidal Zip Lok 400 Aluminium Standing seam roof)

Aluminium supporting frame for planter container supported on aluminium halters

Rigidal Aluminium decking as planter container (0.9mm thk Rigidal 32/167/1000

Aluminium Profile)

Structural Engineering Branch, ArchSD of 15

Issue No./Revision No. : 1/-

Typical Green Roof Section General view of Green Roof prior to filling of soil

Composite mat drain installed Filling of soil and plants

10.4 Installation Details adopted for Tseung Kwan O Complex in Area 44, Tseung Kwan O (TKO Complex)

10.4.1 For TKO Complex, a modular green roof system in the form of plastic trays was installed. The chosen product, Greenlink ML-125 Modular Panel (Figures 5 and 6), is made from 100% recycled High Density Polypropylene resin, and the manufacturer claimed that the system is suitable for use over any type of watertight membrane.

10.4.2 The roof floor at TKO Complex is supported by steel trusses spanning at 41.5m. Similar to TSW-IRC, steel sub-frames and roof decking are installed onto the steel trusses to build up to the required levels and pitch angles. Vapour barrier and insulation are then installed on the roof decking (Refer to Figure 7 for waterproofing details).

10.4.3 A layer of geotextile and a further layer of waterproofing are then applied. The plastic trays are placed on top of the waterproofing membrane to complete the green roof installation. There is no fixing between the green tray and the roof and uplift wind pressure is counterbalanced by the dead load of all the trays linked up together. To minimize the lift up force by the wind, an aluminium edge was installed on four sides to seal up the gap of the tray underneath.



Rigidal Zip Lok Roof

Drain Channel Gutter

0.9mm thk aluminium profile with perforated divider

Greenlink ML-125 Modular Panel

Figure 5: Dimensions of Greenlink ML-125 Modular Panel

Figure 6: Schematic of Modular Green Roof at TKO Complex

10.4.4 The green roof system of TKO Complex is summarized as below (top to bottom):

Green Roof 1. Tray System – Greenlink ML-125 Modular Green Roof System

Building Roof 2. Waterproofing and insulation (Refer to Figure 7)3. Corrugated steel roof decking4. Steel sub-frame to build up to Roof level as required by

ArchitectLong-span Steel Truss Supporting Roof floor



Figure 7: Waterproofing Detail for TKO Complex

10.4.5 The green roof supplier also provides a built-in irrigation system, a layer of non-woven geotextile layer, supporting grille, anti-erosion guard, substrate and plates.

10.4.6 The outside dimension of each standard tray is 528mm x 528mm x 125mm (H). The system has high compressive strength and interlocks so that the units can accommodate changing slopes and curved surfaces. Within each tray, there are three main layers, namely (from top to bottom), (1) Plant level, (2) Substrate soil and (3) Filter sheet.

10.4.7 Installation of the plastic trays is generally carried out by manual labour. The plastic trays are interlocked with each other by pins. Although it is possible to install pre-planted modules, the modules were installed as empty trays to facilitate lifting operation and manual installation.

10.4.8 Some photos of the installation of the green roof system are shown below:

Steel Truss and sub-frame Installation of roof decking



Installation of vapour barrier and insulation Installation of waterproofing membrane

Installation of top protection membrane Positioning of plastic trays

Interlocking of plastic trays Installed Plastic trays

Filling of Soil (Photo taken for a different project, Greenlink website)

Planting of Vegetation (Photo taken for a different project, Greenlink website)



10.5 Installation Details adopted for the Columbarium and Garden of Remembrance at Kiu Tau Road, Wo Hop Shek

10.5.1 The buildings adopted the intensive green roof system with similar installation details on top of the finished roof floor surface (screeding and waterproof membrane). The roof floor itself is constructed of reinforced concrete slab and beam structures and spanning a maximum distance of about 15m between column/wall supports.

10.5.2 Construction of the roof top gardens covering mainly lawn areas and seatings, was carried out according to the architect’s details (refer Figures 8 and 9). The intensive green roof system comprises the following layers (top to bottom):

1. Top soil mix2. Drainage layer, MiraDRAIN 9000 3. 60mm thick C/S screed with BRC4. Insulation board cast with 25mm thick waterproof C/S screed5. Waterproof membrane6. 1:3 C/S screed laid to fall, min. 25mm thick7. RC roof slab and beam supporting structure

Wo Hop Shek Columbarium: Views on Green Roof Garden



Figure 8: Typical Details of Lawn

Figure 9: Typical Details of Roof Garden



10.5.3 Site photos for the installation of green roof system are shown below:

1. Laying waterproof membrane 2. Water test after laying membrane

3. Laying insulation boards 4. Applying cement and sand screeding

5. Laying MiraDRAIN drainage layer 6. Laying sub-soil drain pipes



7. Backfilling of soil 8. Green roof lawn and seatings

10.6 Observations and Discussions

10.6.1 Discussion on the advantages and disadvantages of the plastic tray green roof system can be found in Section 7.2 of the report “Study on Green Roof Application in Hong Kong – Final Report” commissioned by ArchSD and issued by Urbis Limited in 2007. The report can be found at the Intranet web site of Property Services Branch at the following link:

http://psbiis/psb/refer/Health%20Safety%20Environment/Greening%20Corner/Green_Roof_Study-Final_Report.pdf

10.6.2 Construction for both the TSW-ITC and TKO Complex were completed in May 2011. Feedback sought from the respective Project Architects, Clerks of Works and Property Services Managers indicated that there had been no reportable defect on the green roof and waterproofing installation from both projects since their completion up to early 2013.



http://psbiis/psb/refer/Health%20Safety%20Environment/Greening%20Corner/Green_Roof_Study-Final_Report.pdf%20

http://psbiis/psb/refer/Health%20Safety%20Environment/Greening%20Corner/Green_Roof_Study-Final_Report.pdf%20

section 10 - green roof installation details (draft-01)

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