Testing the Limits

TEXT Douglas MacLeod
PHOTOS Structurlam, unless otherwise noted

The two-person crew slams and braces the 2 x 6s into position. First they set down a rectangle of finger-jointed 40-foot-long pieces, spray it with glue, then place a layer of 8-foot-long pieces crosswise over top. A third layer of 40-footers completes the massive wood sandwich. The entire panel is rolled into a hydraulic press. Ninety minutes and 80 psi later, an 8-foot by 40-foot finished product emerges that is changing the way architects think about wood construction. 

“Cross-laminated timber, or CLT, is plywood made from 2 x 6s,” explains Stephen Tolnai, Director of Sales and Marketing at Structurlam, a leading Canadian manufacturer of the product. Built with three, five or seven layers of wood, CLT panels are ready to use as floors, roofs or walls. Using CNC equipment, door and window openings can be cut out in the factory, and on the job site, the panels can be trimmed with a saw. Like light wood-frame construction, cross-laminated timber uses quick-growing species such as spruce, pine and fir, but its layers allow CLT to perform much like heavy timber. The cross-lamination reduces swelling and shrinkage, while strengthening the panels in two directions, in the same manner as a reinforced slab. These properties allow CLT panels to span up to 7.5 metres (25 feet). 

Canadian companies such as Structurlam and CST Innovations are positioning cross-laminated timber as a time-saving replacement for concrete. As Tolnai points out, “CLT is just as strong but one-sixth the weight–and it can be installed in two-thirds the time.” In 2009, for example, a four-man crew assembled the eight-storey superstructure of the Stadthaus apartment block in London, England in just 27 working days, using only a mobile crane. Building eight storeys in concrete could easily take 40 days or more. While architect Andrew Waugh points out that the material was more expensive than reinforced concrete, he emphasizes that labour savings far outweighed material costs.

Equally important are the sustainable features of this product. Wood is a natural carbon sink and a dry cubic metre of Douglas Fir typically sequesters 255 kg of carbon. This property of wood allowed Waugh to argue that his design sequestered 188 tonnes of carbon while a similar concrete building would have generated 124 additional tonnes of carbon through its manufacture. Thus, the use of CLT resulted in a total offset of 310 tonnes. Also significant for British Columbia is the fact that lumber used in CLT panels can include pine beetle-killed wood from lodgepole pines, thus making use of trees that would otherwise be left to rot in the forest. As architect Michael Green of Vancouver and New York has written, “Every great movement in architecture has been born from a structural revolution. Steel and concrete in the industrial revolution gave us Modernism.  Wood in the climate change revolution will offer us a new architecture; one where we either replicate the forms and approaches we have in the past with steel and concrete, or an architecture where we look at all the systems of a building as one–as nature does.” 

Cross-laminated timber has its origins in Switzerland in the 1990s. From there it quickly found acceptance across Europe and particularly in Austria, Germany, Sweden, Norway and the United Kingdom. European companies such as KLH have an annual output of almost 650,000 m2 per year, dwarfing the 200,000 m2 per year (27 panels per day) currently produced by the Structurlam facility in Okanagan Falls, British Columbia.

As Tolnai points out, “We’re really in the early phase of the life cycle of this product. We need innovative architects and early adopters to embrace this new technology.” Fortunately, that’s exactly what’s happening across the country. Currently in Canada, CLT is often used in conjunction with other types of engineered wood. Opened last June, the Elkford Community Conference Centre by Douglas Sollows Architect, one of the first commercial applications of CLT in North America, includes structural insulated panels (SIPs), glulam beams and heavy timber trusses. John Paone, a director of Elkford Centre builders Alfred Norie Construction, emphasizes that proper planning is the key to building with cross-laminated timber. He notes the need for accurate modelling, checking and double-checking details, and organizing the shipment and storage of the material in a manner that allows the “pieces of the puzzle” to be easily and quickly assembled. 

But what of its drawbacks? As its proponents are quick to admit, CLT is ideal for specific kinds of buildings. At almost double the price tag of stick-frame construction, it’s inappropriate for individual homes. As the European experience has shown, CLT is an economical and sustainable alternative for mid-rise buildings up to 12 storeys in height. While architects such as Green argue that various wood technologies can be used as the structure for buildings up to 30 storeys high, CLT will probably never replace concrete and steel for very tall buildings. Finally, it should be noted that CLT does not have the sound-isolating properties of concrete and its spans are limited by the natural deflection of wood under loading.

The major barrier to the widespread use of CLT in Canada, however, is regulatory. While cross-laminated timber has been used in Europe for more than 15 years, it has yet to make it into the Canadian building code system. Each use of CLT requires special approval. Speaking at the 2012 Wood Solutions Fair in Vancouver, Liam Dewar, director of UK timber supplier Eurban, was emphatic that we must “free the tree” and end “the discrimination against timber in Canada.” While more than a dozen CLT buildings are planned or completed nationwide, Canada still lags far behind other parts of the world. In the United Kingdom, Dewar and Eurban alone have worked on close to a dozen CLT buildings ranging from two to eight storeys in height, while in Melbourne, Australia, the 10-storey Forte Tower will soon be the tallest timber apartment building in the world. There is no doubt that revisiting our building codes to accommodate CLT would greatly speed its dissemination and acceptance in this country.

For the time being, promoters of CLT recommend that architects employ specialists early on in the design process. Tolnai, for example, suggests hiring a code consultant to guide the design through its various stages of approval, and engaging a heavy-timber specialist during construction. A variety of organizations are also providing resources to help architects use this product, including FPInnovations, whose comprehensive CLT Handbook covers everything from structural design to vibration performance. 

Despite regulatory challenges, Canadian professionals are already testing the limits of what CLT can do. McFarland Marceau Architects used cross-laminated timber in their Bioenergy Research and Demonstration Project for UBC Vancouver. When asked to design an addition to the Fitness and Wellness Centre at UBC’s Okanagan campus in Kelowna, they wanted to try something new. According to Craig Duffield, the associate in charge, “the idea was to take CLT and use it in an unanticipated way.” In this case, they crafted curved and streamlined moment arches from the material. The column and beam components of the arch are prepared as separate pieces of CLT, then joined with a glued-in HBV shear connector–a steel mesh that fits into a slot cut into both halves. These moment arches demonstrate how CLT can be shaped into complex forms using standard CNC equipment.

Other firms are also exploring the possibilities of wood construction.
Earlier this year, Williamson Chong Architects won the prestigious Professional Prix de Rome in Architecture for their proposal entitled “Living Wood.” Over the course of the next two years, the firm will explore innovative wood products and manufacturing technologies including CLT. As part of their study, they will visit completed buildings and manufacturing facilities from Austria to South Korea.

Composite systems are another powerful area of potential innovation for CLT. Such a system can also be found in the Fitness and Wellness Centre where the architects used a five-ply CLT panel for the floor, covered with one inch of acoustical insulation and four inches of concrete. Here too, HBV shear connectors hold the system together. The resulting floor is both cheaper and lighter than a solid concrete one.

It is in the adaption and combination of this material with other building systems that CLT may demonstrate its real value and help us to revolutionize the role of wood as a natural and sustainable construction material. With Canada’s vast stands of timber, CLT would seem an ideal product to help re-energize our national forestry industry. With the current innovations being designed and built by our architects and engineers, Canada can, and should, play a leadership role in a wood construction revolution. CA

Douglas MacLeod is the Chair of the new RAIC Centre for Architecture at Athabasca University and is an advisor to the CoCo Laboratory, a design, research and development incubator.

The Tall Wood Buildings study is available as a free download from www.mg-architecture.ca/portfolio/tallwood/ and FPInnovations’ CLT handbook may be purchased at www.fpinnovations.ca.