British Columbia is famous for its post-and-beam architecture of cedar, pine, hemlock and fir. But for a growing number of situations, the material of choice is a different kind of wood altogether: cross-laminated timber. The ultra-strong engineered wood is what architect Greg Dowling chose as the main structural material for his own residence. Although a growing number of architects are looking at cross-laminated timber (CLT) for their larger projects, this is the first house in North America to use CLT as the main building material – floors, walls and ceilings – according to Mr. Dowling. “I was the architect, contractor and client all in one, so I had the choice to do it this way,” he says.
Mr. Dowling, a principal at Vancouver-based DGBK Architects, was not only making a home for his family; he was effectively launching a kind of pilot project. Mr. Dowling had heard about CLT used in European high-rises and nascent interest in Canada for the same sort of applications here.
But when it came time to build a house for his wife and teenage daughter, he grew intrigued about the less-common practice of using CLT as a primary building material for a low-rise single family house. Part of the reason, he says, was his perception of the shaky quality of standard family-home construction. He recalls walking around a typical wood-frame and drywalled house and thinking how hollow it sounded when he walked on it, compared with the solidity of CLT. “The more I learned about cross-laminated timber, the more I was convinced I wanted to use it.”
CLT is one of the most intensely discussed building materials in Canada right now. Plainly speaking, CLT is an engineered wood like glulam or plywood. But unlike glulam – which is essentially made of long strands of wood glued together – CLT is made by stacking several sheets of glued wood like a sandwich in alternating layers, which gives it incredible strength that’s comparable to steel, concrete or old-growth timber. That’s why CLT is often simply called “tall timber,” an allusion to the heights it can theoretically be built to. Natural wood can be used for the structural framework of low-rise projects, say three or four storeys, but it’s too weak to build much higher than that. Using CLT as the framework, architects in Britain and Australia have designed buildings nine storeys high. Some, including Vancouver-based Michael Green Architecture, are exploring ways to build even higher, up to 30 storeys.
Although CLT has been used in Europe since the 1990s, it’s still perceived as something of an esoteric material in North America, although that’s changing now. B.C. now has its own CLT-making plant, Penticton-based Structurlam Products LP, which opened last year. Mr. Dowling had planned to source his CLT from Structurlam, but due to a delay, he had to order it from Austria instead. “It made it more expensive, but we couldn’t wait a year,” he says.
With a regional plant now able to provide the product, designing and building with CLT is not particularly complicated or expensive, says Mr. Dowling. CLT is fabricated and cut off-site using highly precise laser-cutting equipment. Unlike conventional wood-frame construction, in CLT construction the cutouts for electrical outlets, pipes and mechanicals must be done in the factory ahead of time, and each CLT component must be very precisely measured and cut to fit. It is essentially a prefab system, which slashes the on-site construction time immensely: Mr. Dowling’s pre-cut CLT panels took roughly six days to assemble on-site. “It would have taken us four or five months with conventional construction,” he notes.
The decision to use CLT also derived from aesthetic considerations, says Mr. Dowling. For his site on a forested, rocky slope in West Vancouver, he wanted a house with a sleek, slender look to contrast artfully with the nature around it. The home’s signature feature is a triangular deck that projects dramatically from the front façade. It’s made of a series of seven-foot-wide, 10-inch-deep CLT planks. “If it were done in concrete,” notes Mr. Dowling, “it would have to be at least 16 inches deep, and require a lot of formwork.”
Although the Dowling House foundation is of conventional concrete, and a small number of walls and columns are made with concrete and steel respectively, CLT is the primary component of the floors, walls, and roofs. Its strength as a supporting or cantilvering material is roughly equal to that of reinforced concrete. Even though CLT is a wood product, it is almost always sheathed in drywall or other material in order to hide its roughness and the pre-cut holes that contain a building’s electrical and mechanical elements. CLT has strong earthquake and fire resistance, with a slow char rate similar to that of heavy timber.
The innovation of the construction material and methodology prompted the West Vancouver Museum to feature the Dowling Residence on its annual summer home tour on July 13. The tour’s co-ordinator, West Vancouver Museum assistant curator Kiriko Watanabe, says the Dowling Residence is right in the tradition of West Coast modernism: “The use of wood in a new way, with the lateset building technology, is clear,” says Ms. Watanabe.
The Home Tour’s four other houses include two mid-century Ron Thom renovated houses, a 1967 renovated Bob Lewis post-and-beam, and the 1979 self-designed Barry Downs residence. All are made of wood, but it’s Mr. Dowling’s house that may well represent the future. And like the other four houses, the Dowling Home is about more than just technology or aesthetics. “Like all five houses in the tour, it exemplifies the formal values of West Coast architecture,” says Ms. Watanabe, “but also the West Coast style of living.”