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Wood: A new framework for sustainable construction

Michael Green Architecture

1st February 2015

Flat-pack construction may bring to mind IKEA home furniture, but using wood to replace concrete and steel as the basis for tall buildings is a viable reality thanks to next generation engineered timber and global advocacy.

Building with wood is nothing new. In the U.S. and elsewhere, the majority of family homes are wood-framed and, until the early 1900s, most commercial buildings were made of timber.

But, the construction of tall buildings using wood as a structural base is something completely different and is being championed on several continents.

In New Zealand where, in the aftermath of the devastating earthquakes of 2010/11, almost a third of the city of Christchurch’s buildings were left severely damaged or destroyed, timber is playing a vital role in reconstruction efforts.

The city’s Central Recovery Plan includes a focus on timber as the main material in a number of projects and, in early 2014, Christchurch welcomed its first multi-storey wooden structure – the Merritt building, located in the city’s CBD.

THE IDEA

Viewed as a safe alternative to traditional construction materials, the building uses post-tensioned technology whereby timber is lashed together with steel tendons that have a similar effect to elastic bands, allowing the building to literally spring back into alignment following any seismic activity.

The brainchild of Dr Andy Buchanan, Professor Emeritus at the University of Canterbury in Christchurch, and his team, the development of the pre-fabricated and glue-laminated box beams and solid columns used in the design, were the result of research into the technology undertaken prior to the 2010 earthquake.

A second timber-based structure, the two-storey hi-tech Trimble building, was unveiled in April 2014, and uses the same post-tensioned technology.

Although New Zealand is a receptive environment when it comes to sustainable design in general, Professor Buchanan says that there are inevitable challenges in translating ideas to reality.

He says: “Many sustainable design options do not make it to the final building because they get cut out along the way as the client tries to save money, during the ‘value engineering’ process.”

Nonetheless, this groundbreaking technology is making waves elsewhere around the world, as he explains: “There is growing world-wide interest in multi-storey timber buildings. One of the main problems to overcome is designing the connections between the beams and columns and other main structural elements. Whereas steel can be welded and concrete can be poured as a liquid, timber connections tend to be more difficult. The Pres-Lam post-tensioned timber building system developed in New Zealand overcomes this problem by making connections with high strength steel tendons passing through the structure.

“We are assisting with the design of a 12 storey building in Ottawa, Canada, right now, using the Pres-Lam system, supported by the Canadian government as part of a design competition to increase the use of timber in tall buildings.”

In the U.S., financial support from the timber industries and political support from the U.S. Agriculture Department has also seen the launch of a similar initiative –the Tall Wood Building Prize Competition.

Buchanan has been advocating the use of wood in building design and construction since 1980, when he returned to New Zealand from Canada after studying timber design at the University of British Columbia.

“Timber design concepts have taken off in the last 10 years with the demand for sustainable construction, coupled with new engineered wood materials and new techniques for connecting timber elements to each other.  Innovative research in New Zealand since 2006 has also greatly enhanced opportunities for multi-storey timber buildings,” he says.

“At the moment I am working with Prestressed Timber Ltd to design new timber buildings. We are continually optimising timber design and construction methods to make tall timber buildings faster and more economical to build,” he adds.

CHALLENGES

The future prospects for increased acceptance and use of wood in tall builds are generally positive, but Buchanan acknowledges that it’s a slow journey. “It is now being recognised that timber can be substituted for steel or concrete in most above-ground building solutions. The biggest market for multi-storey timber buildings is a four, six or eight storey, so that is where the growth will be. Taller timber buildings are also possible, but their economic success has not yet been demonstrated.”

Back in 2013, Chicago-based architecture firm Skidmore, Owings & Merrill  (SOM) released a report on the feasibility of using timber to construct office towers, with the conclusion that combining wood with some concrete reinforcement could be used to construct buildings as tall as 42 storeys (or 395 feet).

One challenge to this argument is the fact that building codes usually permit wooden-based structures of no more than six storeys due to fire regulations and the possibility of buckling under pressure should a natural disaster occurs.

However, architects and engineers are fighting their corner, mooting the application of fire-protective coating for timber frames, the ability of engineering to raise the durability of timber to a level similar to concrete and the benefits of computer modelling in optimising earthquake-resilient design potential.

But, convincing developers and builders to switch to wood continues to be a hard sell. In the end, environmentally minded landlords and tenants looking for buildings that emit less carbon to create and consume less energy to operate will largely dictate the use of timber in construction.

Canadian architect Michael Green, founder of the firm behind the recently launched Wood Innovation & Design Centre in British Columbia, is the author of a 200-page instruction manual, entitled ‘The Case for Tall Wood Buildings’.

Green has distributed free copies to his industry peers in the hope that it will inspire architects and engineers to look beyond concrete and steel and consider timber instead.

As a natural material that sequesters CO2 from the atmosphere, holding up to one tonne per cubic metre of wood captive during its growth and lifetime in a structure, this equates to 3,100 tonnes of non-released CO2 in a 20-storey building as opposed to 1,200 tonnes released by an equivalent concrete structure.