Eco-Office Tower: Navan Credit Union: Ireland

Paul Leech BE BArch (Hons) RIBA MIEI

Paul Leech GAIA ecotecture / GAIA International, 11 Upr Mount Street, Dublin 2, Ireland.

Tel +353 1 661095 fax+353 1 6785124: paulleech@eircom.net

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KEY POINTS: three pillars of sustainability; social, economic and ecological.

- multi storey timber structure: office building : 30 metre: brettstapel technique.

- Naturally ventilated, assisted by passive solar chimney. Passive cooling/ night purging.

- Low embodied energy: Limecrete :baubiologie breathing fabric: rainwater capture

- Building Energy Management System; 50 kwhrs/m2 /yr:'green' grid electricity

INTRODUCTION

A highly successful Credit Union, (being a community financial services organisation),

proposes a high quality second-phase building on ‘deep’ green principles. This will be an

extension to the earlier (first phase) building, which may be characterised as ‘light’ green,

completed in 1988, designed by the same architect (1). The project consists of six

accommodation floors above ground with two ancillary/ plant room levels in the attenuated

‘attic’ spaces. There is an external lift tower, some single storey volumes at ground level,

including a ‘garden pavilion’, banking hall, extending into the existing ‘peace garden’ with a

new roof terrace over this.The apex of the tower is given over to a community room, an

interpretative display on the history and the functioning of the Credit Union movement and

the environmental performance of the building. Access to this room (over the Manager’s

office) will be freely available to Members and visitors. This will provide a striking view

longitudinally along the proposed new Civic Space. Therefore, from both inside and outside

the sense of member’s ownership of the building is emphasised, providing a revived civic

perspective. The external elevator is designed with a vision aperture to provide an enjoyable,

dynamic but secure experience (this is a low energy elevator, eg. by Kone)

ARCHITECTURAL / URBAN DESIGN CONTEXT

Photomontage Urban Towers Aerial View in context

This is a town centre building that attempts to add to macro townscape quality as a ‘landmark’

building for the 21st century, the vertical concomitant of the horizontal and longitudinal

proposed Civic Space (see photomontage above, into civic space site- currently an ugly car

park). The tower form has a symbolic townscape role in a degraded and now sprawling town,

which is losing the quality of its historic core. It abstractly emulates the form language of the

existing two church towers in the old town. Practical matters of a very confined site and

difficult context also support the tower idea, which is unusual (for us) and requires rigorous

justification.

TECHNICAL DESCRIPTION:

Terracotta rain screen cladding: Holzbau/ Brettstapel: limited kerto elements

Fire Safety

This matter received very close attention from an early design stage. A fire-engineering

approach has been adopted and kept under review. Preliminary discussions were held with the

Fire Officer, several experts have been consulted (4) (5) and conclusions have been reached,

eg. the maximum height of habitable floor plate is 18 metres above ground (the fire station is

adjacent and ladder reaches max.30 metres): Misting sprinkler system as recommended in US

standards: Firefighting lift: Very high standard of detection and alarm: Low occupancy rooms

only above 1st floor.

If carefully designed, timber structures of this height have been established by our design

process to date as being feasible. Each jurisdictions has its own protocols and these must be

checked on a case by case basis by designers as tests applied from first principles. Timbers

structures usually depend on steel or other metal connectors. Apart from our target of low

embodied energy, the issue can also be problematic in relation to fire, with the early failure of

connections between massive timber components. In this respect, the brettstapel system being

used by Merkle Holzbau of Bissingen Teck (7) is of great interest. In this system, beech

dowels (at 8% moisture content) are inserted, under pressure, through slightly smaller

drillings (typically at 12%MC): As the moisture contents equalise, they become an integral

solid timber construction, with attractive fire safety characteristics, while retaining very low

embodied energy. This component is manufactured to a quality control level that allows it to

be used, as an exemplary product, worthy of support from the demand side. The downsides of

transportation across Europe are, in our view, outweighed by the benefits of demonstrating

this technology in Ireland. Surface Spread of Flame is a key issue and may be addressed with

specialised coatings where required: care must be taken to minimise the use of any toxic

substances; other fire-engineering measures may be preferred.

There is also a synergy between fire safety and acoustic considerations in massive composite

timber construction. The use of imperforate fire barrier ceilings of non-combustible material

with the services zone above the floor is proposed. These provide mass to damp airborne

sound (14).

Transport

The Credit Union will encourage a modal split away from the private car by providing very

restricted private parking and generous, secure, bicycle-parking facilities attractively designed for

both members and staff. Within the building, generous showers, changing and locker facilities

acknowledge the needs of staff who opt for this more sustainable and healthy mode of transport,

reducing traffic congestion and pollution.

Timber Frame Construction.

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This would be, we understand, the tallest timber-framed office building in the world. Historic

timber structures may have exceeded this in height, but we are demonstrating feasibility

within contemporary practice, regulations and standards. Two types of structural system are

being explored: One is a rigid plate box of brettstapel construction with no frame.The other is

a framed structure of Kerto/ Glulam with bretstapel infill. The former is preferable by

ecological criteria, as glues are avoided. Detail design, calculations and modelling will

establish the optimum, structurally. Calculations have been carried out to establish that the

structure is in fact feasible in its present configuration (5) (7) and indicate further design in

detail of connections etc.

Remarks of Gardiner & Theobald: Building Cost Consultants.

”The project consists of a mixture of new build, fit-out and refurbishment work,total budget

of 4,376,787, including taxes, inflation but excluding professional fees and cost of land: new

build area of 844m2. The costings reflect the project status up to detailed planning stage and

were in all cases based on detailed discussions with specialist providers. The scheme was

benchmarked against “developer standard office space” using traditional methodologies,

materials and components. The proposed tower would cost in the order of 1,700,000

including taxes in excess of the conventional benchmark. The factors, which created this

divergence, fall into two broad categories;

(a)Site Logistics and site Abnormals: The proposed site is limited in terms of size, access

and proximity of adjacent occupied spaces, all of which created adverse cost issues which, in

turn, were compounded by known poor ground conditions. However the key additional cost

arose from the high Wall to floor ratio at 1.0, which created a disproportionate envelope cost,

structural frame cost and relative diseconomies due to the number of floors: The tower form

is not justified on pure economic criteria.

(b) Added Value: At the outset the client embraced an holistic approach to design and life

cycle cost and consequently considered and approved specification initiatives which would

not form part of the typical “developer standard proposal”. Aside from environmental

considerations this proposal also makes sense from a site logistic perspective because of a

lack of space and speed of ercetion. The timberframe created a significant additional cost,

which is attributable to the lack of competitive market in Ireland for products of this nature.”

Remarks / Drawings of Pirmin Jung, Structural consultant, on behalf of Merkle

Holzbau (7)

“With the Office Tower project, we are dealing with an innovative building which, with its

execution, would have a far reaching global effect on the future of multi storied timber

constructions. With the latest timber construction techniques, 8 storeys are absolutely

possible.

The principle issue for the construction of the building does not lie in the vertical load but

much more in the rigidity required by the slenderness of the building to withstand the wind

factors. The effects due to vertical load in the required walls are separated from loads due to

wind effects.

Fire protection can be fulfilled through assessment of burn up and encasement of the

supporting structures. Increased sound insulation can be derived with the appropriate

encasement of the building elements.

An 8 storey timber construction building can only be ideally constructed when both the

architectural elements and statics are already integrated in the preliminary project. Therefore,

early cooperation and planning between timber construction engineers and architects is

essential.

Remarks of Derham McPhillips: Joseph Rooney, Environmental Services Engineer.

The use of low energy, high frequency light fittings was proposed throughout the building

with photocells switching and controlling the number of lights switched on. Controlled

dimming was considered but rejected because of cost. Positions of all proposed electrical

equipment was closely monitored to reduce the effect of electromagnetic fields. A PV panel

on the roof provided limited power for ventilation. Various mechanical options, including

combined heat & power plant, thermal storage & geothermal heat pumps were initially

considered but were rejected after cost benefit analysis. Air conditioning was also considered

but rejected because of its high energy demand. Underfloor heating and wall heating were

considered. Finally a combination of a condensing boiler with radiator circuits and a

sophisticated natural ventilation system was accepted as providing the best solution. The

natural ventilation system used a full height vertical duct linked to a solar chimney. Each

room was connected to this vertical exhaust duct by ceiling ducts. The solar chimney

provided the negative pressure within the building. Supply air was brought into the building

through the external walls. This air could be preheated as it passed over heating coils where it

entered the building. There was also provision to bring cooled air into the building by drawing

the inlet air over a pond in a garden outside the building. The speed of movement within the

vertical duct was controlled by motorised dampers. The hot water solar panels, which

provided preheated water for the calorifiers, was also linked to pipework surrounding part of

the solar chimney to help generate upward air movement in the vertical duct. A small fan was

also placed in a bypass of the solar chimney to provide air movement in poor weather

conditions. A sophisticated BEMS was proposed to control the complete M & E installation

including the motorised dampers for air movement: Night time purging would also be

controlled by the dampers. Manual over-rides would be available in each room to give staff

individual control, thereby widening the comfort band.

References

(1) Plan Magazine Ireland: May 1988: Also Build Magazine Ireland March 1988

(2) Van Der Linden MLR 1999 “Timber Concrete Composite Floor Systems” Delft Uni Press

ISBN90 407 1979 9

(3) Aicher, S (editor) COST Action E5 Otto Graf Institute ”Timber-Concrete Floors”

(4) Fontana, Professor Doctor Mario: Zurich ETH: personal Consultation Zurich 2001

(5) Sigrist, Prof. Dr.Christophe: Biel School of TimberEngineering, Switzerland: Personal

Consultationat Bieland correspondence, 2001: includes Work of Postgraduate students;

Martin Ruedisuehli, Christian Schoop, Jakob Studhalter.

(6) Roalkvam, Dag: 1997 av siv ark GAIA LISTA: Member GAIA International |NABU

Norway (Chris.Butters@arkitektur.no). “Naturlig Ventilasjon”

(7) Merkle Holzbau GMBH Fabrikstrasse 31 73266 Bissingen/ Teck tel. 07023/900590

advised by Pirmin Jung, consulting engineers Ingenieure für Holzbau GmbH Chänelmatt

10

CH - 6026 Rain info@pirminjung.ch

(8) Haring, Chris Herman Dipl.Ing. ETH/SIA info@haring.ch: personal consulatation 2001

(9) Kauffman Holz Ag Austria tel 00 43 557 48040

(10) Merk Holzbau info@merk.de

(11) Derham McPhillips: Consulting Engineers, Dublin Ireland (dmp@indigo.ie)

(12) Gardiner and Theobald: Quantity Surveyors (www.gardiner.com)

(13) Berge, Bjorn: GAIA Lista 2000 Architectural Press ISBN 0 7506 3394 8 “Ecology of

Building Materials” member GAIA International

(14) Hammer, Peter: (editor) 1998 ISBN 0 86282 111 0 “ Acoustic Performance of Medium

Rise Timber Buildings” COST Action E5 Workshop

(15) IABSE Conference Report: Lahti Finland 2001 ISBN 3 85748 1003 X “Innovative

Wooden Structures and Bridges”