Steel and concrete, the bigger the better, damn the ecological torpedoes – full speed ahead! That’s just so last century. Urban growth in our future may well be built on a more human scale than kabillion-storey skyscrapers. The growing consensus is that mid-rise, mixed-use development represents the new wave, in part fuelled by eco-consciousness from the consumer level right up to the highest government echelons. New climate policies coming into place stress carbon-neutral and even carbon-negative alternatives to current construction methods that rack up emissions faster than a fat kid tearing through a sack of Halloween candy.
For an innovative group of builders and architects, mostly in Europe and on Canada’s West Coast, the answer is obvious: wood. Or rather, cross-laminated timber (CLT), wherein powerful adhesives are used to bond together huge panels with the commensurate strength of steel and durability of concrete at one-fifth the weight. CLTs, also known as mass timber, have a small carbon footprint and a sublime recycling afterlife. Wood too is a natural, cost-efficient trap for carbon dioxide, providing those negative emissions so necessary to achieving Paris Climate Agreement – and new LEED V4 Gold – goals.
According to the aptly named Vancouver architect, Michael Green, speaking in a recent TED Talk: “If we built a 20-storey building out of cement and concrete, the process would result in 1,200 tons of carbon dioxide. If we did it in wood, we’d sequester about 3,100 tons, for a net difference of 4,300 tons. That’s the equivalent of about 900 cars removed from the road in one year.”
Oliver Lang, principal at Vancouver’s Lang Wilson Practice in Architecture Culture, says the ecological benefits weigh heavily in refined lumber’s favour. In June, Lang co-presented with the University of British Columbia (UBC) at the Canada Green Building Council (CaGBC) conference in Toronto. Wood Buildings – Moving from Prototype to Mainstream explored the rationale for timber as an infinitely renewable resource that can be sustainably harvested. Moreover, in Canada at least, this regionally available material offers great economic potential to local communities. Rather than being proverbial hewers of wood (that’s shipped across the world mostly to make simple two-by-four concrete forms which end up in landfills), Canadians could process the lumber themselves into customized, prefab slabs and columns and then ship the pieces out to be assembled like Lego onsite. The cost advantage and jobs created could give a big bump to both our GDP and our global reputation.
Speaking of global reputation, the UBC, in conjunction with Vancouver-based Acton Ostry Architects, is currently working on the interior finish of the tallest mass-timber hybrid building in the world. The Brock Commons Student Residence began construction in November 2015 with a slated completion date of September 2017. The 18-storey, 53-meter-tall structure – limited in size only by the university’s Land Use Plan – will house over 400 students. It will also act as a living lab for UBC’s engineering, architectural and scientific faculties, who will monitor various factors of the building’s long-term effectiveness.
Go to Brock
Brock Commons was the result of a Natural Resources Canada competition that the UBC won, in part because of their previous experience with erecting four- and five-storey mass-timber buildings on campus. John Metras, the university’s managing director of infrastructure development, says the $51.5 million hybrid project could have been made entirely out of mass timber: “But we took a relatively conservative approach in the design to ensure we had the social license for it – that is, public acceptance of the concept. We’re trying to demonstrate applicability of wood in the most practical manner. The most efficient design involved steel connectors between the timber columns, and the use of a concrete podium and elevator cores, for stability and seismic performance.”
While the residence exceeds provincial earthquake parameters, Metras says the issue of fire is no issue at all. Unlike steel beams, which can melt or contort in a blaze, “mass timber is not like your typical two-by-fours. These are large, engineered components. They don’t really burn. A fire would cause charring but the timber would retain structural integrity.” However, to allay any student and parental fears, “we encapsulated the entire structure with up to three layers of fire-rated drywall. We also installed a back-up water reservoir in the building so if there were an issue of water supply from the mains, the sprinklers would have their own resources.” The high-performance building envelope made from composite wood fibre and resin has also been treated with a water sealer, for extra moisture protection.
The designing, planning and testing of something that has never been done before did involve extra cost. Metras estimates this as an eight per cent premium, what he calls “the cost of innovation,” because it includes extra charges that future projects might not incur. “We built a two-storey, full-scale mock-up of the structure to test the components and design. We tested out several design options for steel connectors that helped us arrive at the most efficient solution, which was a concrete core with an attached wood structure integrated with steel ledgers and drag straps embedded in the concrete to support each adjacent floor panel. At each floor level, we used CLT for panels and glulam [adhered-wood] columns. At each floor plate, a steel connector joins the column below with the column above. This allows the transfer of vertical load to go down through the columns and not place stress on the horizontal CLT panels.”
B.C.’s Structurlam Products, a global leader in CLT and glulam production, was heavily involved in the Brock Commons project. The residence has now been added to the company’s impressive portfolio, which includes the Frank Gehry-designed Art Gallery of Ontario façade, the Vancouver 2010 Olympic Oval and the just-completed Rocky Ridge Recreation Centre in Calgary. The latter building boasts the biggest wood roof in North America – 250,000 square feet, constructed entirely of glulam beams. “It took us a year to manufacture them,” says Structurlam’s president, Bill Downing.
The Brock Commons project, on the other hand, involved far less time and effort than everybody had originally supposed – perhaps a result of all the pre-construction testing and planning. “It’s generated a lot of interest in the local design community,” Dowling says. “They’ve recognized that you can assemble a wood structure very quickly with prefab components. It only took nine-and-a-half weeks to build Brock’s wood structure. They were able to build two floors a week, not one floor, as originally planned. The opening target is now May 2017, advanced from the original target of September 2017.”
Because the material for Brock Commons was completely prefabricated and shipped to the site, only nine workers were required to put the whole building together (fascinating speeded-up footage of the construction is available on YouTube under “Brock Commons Time Lapse”). With nothing else to construct on-site, the workplace, Dowling adds, was uncannily quiet, safe and clean.
So, how far can tall-wood buildings go? “From an engineering prospective,” Dowling says, “30 storeys seems to be the limit. The sweet spot is in the eight to 12-storey range, in terms of cost-effectiveness.” The real challenge is weaning builders from their pricey steel-and-concrete skyscraper diet.
Even if the world changed tomorrow, British Columbia’s mass-timber advocates say our sustainable forests wouldn’t be under attack from CLTs. In fact, according to Structurlam’s background material, there are “more trees right now in the forest that we can use than we did 50 years ago,” including those threatened by rot, fire and pine beetle infestation that can be given new life as building materials.
But put all that science and engineering aside for a moment and simply ask yourself: What could be more beautiful, or indeed more Canadian, than a structure built from our greatest natural resource?