New Zealand Office Project ‘Cracks Code’ for Mass Timber Viability

Warren and Mahoney’s design for New Zealand’s largest mass timber office building at Tauranga was delivered under budget by developer Willis Bond and builder LT McGuinness. Head of design and principal at Warren and Mahoney Blair Johnston believes the architects have now cracked the code on commercially viable mass timber construction by abandoning conventional design processes and prioritising low-carbon outcomes over architectural aesthetics. “We didn’t design a building form or a shape and then decide to figure out how it would be built,” Johnston tells The Urban Developer . “We started with the idea that this would be a timber building and we engineered everything else around that.” The 10,400sq m eight-storey commercial building at 90 Devonport Road achieved a 6 Star Green Star rating and more than 60 per cent reduction in all-of-life carbon footprint. All of this while maintaining cost efficiency through what Johnston describes as a “balanced rather than fundamentalist approach to timber construction”. Laminated veneer lumber—cross laminated timber and glulam—comprises 90 to 95 per cent of the building, including floors, columns, cores, stairs and gravity structures. ▲ Warren and Mahoney head of design and principal Blair Johnston. Steel was used strategically for lateral earthquake bracing in the seismically active region. “That clarity separating those two elements enabled us to achieve a really simple logic,” Johnston says. “The building is an innovative outcome using quite primitive techniques, carpentry techniques, almost traditional techniques.” Back to basics Connection details, such as complex bespoke steel bracketry requiring fabrication and fire rating, typically create cost blowouts in timber buildings. This project avoided those complications by going back to basics. “Our experience with timber buildings has been that where they become really challenging is when you’re joining the timber elements together,” Johnston says. “This building uses more traditional woodworking techniques—overlaying secondary and primary beams, screwing them together without brackets and plugging joints with timber for fire rating.” Repeating the same design across all eight levels reduced costs in the supply chain and on timber milling. The lighter timber construction required less foundation work in Tauranga’s weak soil, balancing out any extra timber costs. Services penetrations, pipe penetrations and sprinklers—traditional challenges in timber construction—were accommodated through structural design rather than afterthought modifications. Structural engineers Dunning Thornton and services engineers Beca worked with the design team from project inception to resolve technical challenges early in the process. Delete De-risking by innovation Willis Bond and Warren and Mahoney promoted a “safe risk” strategy during concept design, developing two parallel schemes—one traditional and one low carbon—through to the end of concept design. The dual approach gave the client time to assess the viability of mass timber construction while addressing potential issues before committing. “That was really valuable, extending that decision point,” Johnston says. “Super valuable to enable the project to proceed in the way it did.” Warren and Mahoney has been carbon neutral since 2007. Johnston says delivering cost-effective low-carbon buildings requires prioritising environmental outcomes over design aesthetics which some clients find “difficult”. “As an architect you’ve set aside to a degree aesthetic aspiration, maybe architectural ego, because actually what you’re trying to achieve is something which is a higher order than those things,” Johnston says. LT McGuinness was initially “cautious” about timber construction but now advocates strongly for the method after experiencing benefits including quieter sites, improved safety and prefabrication processes that resolve issues before materials reach the construction site. Willis Bond director Wayne Silver says the group had “led the way in mass timber office buildings, demonstrating that with careful planning, this approach can be both cost-effective and environmentally responsible”. The Tauranga City Council has leased the building, consolidating staff previously spread across multiple locations. Johnston says the exposed timber creates a residential quality that makes the workplace feel less corporate. Delete Tauranga’s position as a major timber exporting region influenced material selection. The project used a wholly New Zealand supply chain with chain-of-custody certification. Collaborative co-design processes with local iwi—local Māori groups—aligned sustainable outcomes with indigenous values. Is this replicable? Johnston says the project proves low-carbon buildings can meet real-world budget constraints, creating what Willis Bond considers valuable knowledge for future developments. “When we look at it, we are actually working on a lot of timber projects now, particularly in Australia,” he says. “The opportunity to learn and test ideas as a result of this project have been super important. “We can now apply those lessons around achieving low carbon outcomes within real world constraints and different contexts.” Commercial timber construction faces economic headwinds in New Zealand where lower rental rates and higher building costs create tight margins. Johnston says sustainable features often become optional extras rather than standard requirements. “Sometimes sustainable outcomes can be a luxury not a requirement,” Johnston says. “That’s why I think this project’s important, because it demonstrates that you can have both.”

New Zealand Office Project ‘Cracks Code’ for Mass Timber Viability

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