August 1, 2013
by Elsa Lam
A rendering of a 20-storey wood building with a wood structural core and a glulam curtain wall. From “The Case for Tall Wood Buildings”
Tall buildings are a big deal–in more than one sense–in current Canadian construction. Toronto is an epicentre, the top city west of Istanbul for current highrise development. And innovation is happening across the country. The Chicago-based Council on Tall Buildings and Urban Habitat named The Bow in Calgary “Best Tall Building in the Americas” for 2013. Last year’s title went to the twisting Absolute Towers in Mississauga. The ultra-energy-efficient Manitoba Hydro Place in Winnipeg snagged the accolade in 2009.
Canada’s next major construction advance may well combine our modern track record for award-winning towers with our national myth of backwoods origins. Mid-rise wood buildings are now permitted in several provinces, and the next push could be to go even taller. According to studies led by British Columbia architect Michael Green, building up to 30 storeys in wood is both technically and economically feasible. Moreover, building wood skyscrapers could help mitigate global climate change. Steel and concrete production is responsible for about 8 percent of global greenhouse gas emissions; wood, when preserved as part of buildings, stores carbon dioxide.
In February, Green presented his argument for building wood skyscrapers at the TED conference, a popular showcase for thought leaders. Since the video of his talk was posted online last week, over 250,000 people have viewed it.
Green points to the emotional draw of wood–each piece as unique as a fingerprint–but, judging by posted comments, perhaps passes too quickly over the issue of fire. Canadian designers are still haunted by the spectre of a 2011 fire in Richmond, BC, which destroyed an in-construction housing project intended as an exemplar for six-storey wood buildings. Despite the builder’s insistence that the incident pointed to the need for greater fire protection in the vulnerable construction phase–in the finished building, sprinklers, firewalls, and fire separations would have mitigated damage–the image of a wood building burned to the ground touches a core fear that’s tough to dispel.
The peer-reviewed report that grounds Green’s TED talk, entitled The Case for Tall Wood Buildings, does much better in laying out the argument that wood highrises can be durable and safe. It does so primarily by making a key differentiation between light-frame wood construction and the composite wood panels now coming to market. Massive wood products such as cross-laminated timber, Green and his collaborators explain, perform like heavy timber in fires, first charring on the outside in a way that protects the core from collapse. Because of this characteristic, a properly engineered tall wood building can achieve a two-hour fire rating. This would make it comparable in fire performance to steel-frame and steel-reinforced concrete buildings; under sufficient heat, even steel members are prone to collapse.
At the report’s core is a detailed case study design. It lays out engineer-vetted options for 12-, 20- and 30-storey constructions that combine tilt-up structural wood panel products and glulam columns in various combinations. Steel beams support wood floors, providing the requisite level of ductility for earthquake resistance. The designs carry a Creative Commons licence, inviting other designers and engineers to build on the research and share their findings.
As a next step in developing tall wood systems, the report calls for a courageous public-private partnership to construct a pilot project. “A prototype of 16-20 storeys or higher would illustrate the capacity of the system well beyond the approaches used elsewhere,” it notes. Canadian industry and regulators would be wise to step up to the plate, and situate the country as a continued leader in tall building innovation.
Elsa Lam [email protected]