Wood frame construction soars to new heights

Wood frame construction is going up… way up. Now underway at UBC, the Brock Commons student residence is not only B.C.'s first 18-storey, wood frame building but is poised to become the tallest in the world using cross-laminated timber (CLT) technology.

Also known as mass timber construction, the premise according to Paul Fast, founding partner of Fast + Epp, is “not rocket science.” In Europe, they’ve been using this type of building methodology for over two decades with Norway currently holding the record of 14 storeys.

At present, however, B.C.’s less enlightened building code limits the height of wood frame structures to a maximum of six storeys. It was only by virtue of an innovative collaboration between UBC Properties Trust – the entity with jurisdiction over projects built on UBC land – the provincial government, and the Building Safety and Standards Branch of BC (BSSBC) that this project received an official go ahead via site specific, one-of-a-kind regulatory approval.

Simple, sustainable and safe

Despite the complex technology, there’s an elegant simplicity to CLT construction. At Brock Commons, six-in. thick flooring panels made from cross laminated timbers — usually 10 ft. wide by up to 40 ft. long – are prefabricated off-site ready to be set on each floor’s glue-laminated support columns. Next, a crane lifts wall panels — also prefabricated complete with window and door openings, insulation, and electrical – into place where they’re secured with specially designed closures. The process is so efficient that Fast predicts completing a minimum of one floor per week – although he hopes that number will be doubled.

And there are numerous other reasons, both technical and aesthetic, why Fast believes mass timber construction using CLT is a viable alternative to traditional “stick-on-stick” construction or even the concrete and steel design that’s currently considered the sole highrise option.

Cross laminate timber is made from wood that’s 100 per cent locally sourced. It’s a renewable resource, one that Fast notes is now being managed more carefully than in centuries and decades past. It’s more stable than dimensional lumber and doesn’t shrink or warp. When it comes to acoustic resistance (a.k.a. soundproofing), CLT’s thickness and density outperform conventional stick-frame construction.

Wood is also a natural carbon sequester – the environmental math is compelling. As it grows, wood removes carbon from the atmosphere and then stores it indefinitely — thus helping to mitigate global greenhouse gas emissions. On the other hand, every ton of cement produced releases approximately the equivalent amount of CO2 and greenhouse gases into the atmosphere.

Fast stresses that the common concern mass timber structures are dangerously susceptible to fire is a misperception – in fact, CLT is far safer than light wood framing. “Think about a campfire,” he explains. “You wouldn’t start with a big, solid log because you’d never get it to light. You’d use small pieces of wood as kindling and in no time you’ll get a nice roaring blaze. Light wood frame structures, which consist of pieces of dimensional lumber spaced apart with wood sheathing, are more like kindling – mass timber is like the log.” Even if CLT does catch fire, its natural charring effect significantly retards the burn rate because it prevents oxygen from reaching the centre of the wood.

Looking ahead

Although Fast acknowledges that current CLT construction techniques aren’t yet suitable for units requiring a larger square footage, he sees a bright future as the technology evolves and demand rises. He predicts once economy of scale kicks in, B.C. can look forward to a cost effective, sustainable alternative for higher density living. As a final bonus, he notes that research now suggests exposed wood creates a warm, inviting environment that actually reduces stress.

“In my opinion wood is the greenest building material there is. But we need to abandon the ‘old ways’ of thinking about and designing with wood. Then we can build on a growing movement of mass timber design that began in Europe and is continuing in North America.”