Overview
Entrant:
Irving Smith Architects Ltd
Category:
13. Hybrid Building Award
Photographed by:
Patrick Reynolds
Key team members:
Architecture - Irving Smith Architects Ltd
Contractor - Coman Construction Ltd
Structural Engineer - Structex
Services Engineer - Jacksons
Fire Engineer - BCD
Project Management - Aesculus
QS - BBD
Go looking for structural timber buildings in the city and, inevitably, you arrive at a campus or large city site. Fire rating presents a limitation to timber buildings on small city sites; timber requires fire rated claddings and therefore separation from neighbours to enable access for the claddings to be maintained.
At a time when the climate emergency demands carbon responsible methodologies, this requirement for campus or large city sites prompts structural timber buildings increasing in size, complexity, and budget at the risk of exclusivity (Ball-dresses?).
This building considers how we might increase the utilisation of timber in our construction industry by making more structural timber buildings on smaller, central sites (T-Shirts!).
51-55 Bridge Street is a development aimed at commercial and office tenancies. The building comprises 1920 square metres across two full levels and a partial upper floor. Site occupies three former narrow commercial lots, spanning from Bridge Street to the public carpark behind. The building is conceived as five standalone tenancies, interconnected by a shared internal street with integral elevator and stair access.
Completed, the building supports commercial tenants across two levels at its north and south edge and the developers’ relocated offices to the upper ‘penthouse.’ The internal street enhances connectivity of this new build to Central Nelson. Access to all tenancy spaces is afforded and vertical circulation is provided within a triple height space with top lighting to expressed timber structure within.
At each street elevation, a shaped screen formed from perforated metal sheet, folded to form a self-supporting triangular pattern, provides privacy at the southern elevation, and important shaded ventilation to the north.
The building employs a Hybrid engineered timber structural system. This represents a upscaled development of ISA’s recent office building (Wall-E).
This Hybrid Concrete Timber design uses concrete foundation, slab, and perimeter walls to meet geotechnical, fire resistance and weather tightness requirements at the buildings edge. Structural Posts, Beams, Floors and Stairs use a combination of Laminated Veneer Lumber (LVL) and Cross Laminated Timber (CLT).
Timber Structures have been left exposed and expressed throughout the development.
Subsequent building fitouts (by others at the lower floors) have embraced this building aesthetic, retaining exposed and expressed structure to private and public space.
A single, flitched Timber / Steel Cross Brace at either end combines with a central concrete lift and services tower to brace the building laterally. With less concrete and steel, 1920m2 of commercial floor area has a reduced carbon footprint compared to a typical steel and concrete model in the order of 480,000kgCO₂-eq or 250kgCO₂eq/m2.
The carbon benefits are similar in scale to the SCION Timber Innovation Hub. However, there are of course, multiple small city sites for every campus or large site. And, of course, many more developers able to afford T-shirts than ball-dresses.