October 30, 2009
FEATURE | Building and trade contracting
Hybrid building systems could mean a return for wood in ICI projects
The Canadian wood products industry wants to increase market share in the industrial/commercial/institutional sector of the construction industry. While dominant in the homebuilding sector, wood has been effectively barred from the ICI sector because of its flammability.
But evolving technology, changes in building codes and environmental concerns have opened doors.
Now, the wood industry has developed an information program talking to architects and engineers about hybrid building systems that could involve building with a mix of construction materials, like steel and wood, or concrete and wood, or all three.
Steven Street, a technical director with Ontario Wood Works, an awareness program of the Canadian Wood Council, says it could mean “reinterpreting post and beam construction in a much more modern way, and getting more out of building systems that currently exist or are on the horizon for North America.”
While wood typically accounts for about 90 per cent of the houses built in Canada, he says., the growth area is the ICI sector.
The industry was encouraged last April when the British Columbia government revised the provincial building code to allow for wood-frame residential buildings of up to six storeys.
He credits the European industry for taking the lead with the development of cross-laminated timber (CLT) which he describes as “a very, very strong, reinvented wood product.”
CLT has been described as “super-sized plywood,” or “plywood on steroids.” It consists of layers laminated with the grain of the wood at right-angles to the grain in the layers above and below. A typical wall panel might be five of six centimeters thick, making it much more like timber planking than plywood. And it can be laminated to much greater thicknesses, making it much more like square-cut timbers.
“It behaves a bit like a concrete slab,” he says. “It has two-way biaxial loading—very strong in both directions.”
It is also highly resistant to fire and poitn s to a recently completed nine-storey mixed-use building in England built with CLT panels which has no sprinklers.
“The beauty of CLT is that it has the characteristics of heavy timber. CLT wall panels give you a 1 <0x00BD> hour fire rating,” he says. “It’s a very different way of looking at fire and containment.”
The relatively recent move to performance-based building codes in Canada could open the way for greater use of wood., he says.
He notes Part 9 of the code dealing with residential construction remains “very prescriptive” though there are innovations in other parts.
Prescriptive codes tend to lay out a body of rules wheras performance-based codes, in contrast, specify the desired results,and leave it to the architects and engineers meet it.
The latter results in “new systems that engineers can believe in, and can prove performance,” he says.
“That’s where we feel that structures that could be built with a system like CLT would get accepted as an alternative solutions.”
Research in CLT and other wood products is continuing, much of it under the umbrella of FP Innovations, an amalgamation of research organizations into a single non-profit company with research laboratories in Quebec City, Montreal and Vancouver.
Emerging environmental concerns might also speed the acceptance of systems like CLT, Street says, because half of a tree’s mass is carbon and wood products like CLT embody a lot of carbon.
So, Street says, “if you’re doing a sustainable building you can calculate how much carbon is being sequestered.”
The next step would be to judge buildings on their carbon footprint.
“The more the building material can take in, the better it is for that building.”
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