November 8, 2012
As the building industry has grown more knowledgeable about sustainability in the past two decades, it has become highly evident that choices about materials can have profound environmental consequences. Increased sensitivity toward this issue has begun to bring forth innovative ideas and technologies. One such solution, new advanced wood building systems, has been rapidly gaining acceptance in many parts of the world, particularly in the realm of commercial construction, which was dominated by energy-intensive concrete and steel throughout the 20th century. The United States, however, has yet to embrace wood’s potential.
Wood offers three critical environmental advantages over conventional structural materials: it sequesters carbon dioxide, is naturally renewing, and can be recycled for a variety of uses (including biomass for energy production). Because the materials used for the majority of commercial structures of the past century require invasive extraction, energy-intensive production techniques, and highly polluting chemical mixing processes, wood — when properly executed — offers an advantage.
It also provides excellent operational benefits. State-of-the art computer numerical control (CNC) fabrication techniques allow for extreme precision in construction, meaning fewer gaps for unwanted building envelope air leaks, while its inherent material properties help achieve excellent thermal performance.
In addition, wood construction can reduce the environmental fallout from the mountain pine beetle infestation that has devastated parts of western Canada and the United States. When affected trees decompose in place, they release carbon back into the atmosphere; pine beetle-damaged wood is currently British Columbia’s largest source of C02 emissions. When used in construction, however, they continue to serve as carbon repositories.
In addition to its sustainability benefits, wood can help create an architecture of place. In an era of big-box landscapes that render parts of Atlanta and Boise virtually indistinguishable, wood’s warmth and beauty can help architects and designers make buildings that are more closely tied to their context.
Within the past 15 years, wood’s potential has expanded dramatically. In the 1990s, researchers in the forests of Austria began seeking ways to increase its market share in construction with respect to materials such as precast concrete. Led by institutes such as Graz University of Technology, researchers developed a revolutionary new engineered wood panel product: cross-laminated timber, or CLT.
CLT consists of wide, flat dimensioned lumber boards. Fabricators place the boards next to one another, applying glue to the surface. Additional layers are then built on top, each perpendicular to the one below. When pressure is applied to the resulting stack, a large, load-rated structural panel is born.
This new material offers significant advantages over wooden building products of the past. Whereas traditional methods of timber construction are extremely time- and labor-intensive, CLT lends itself extremely well to prefabrication, which can make construction cheaper, faster, of higher quality, and more environmentally friendly. It can easily be cut to the required size and shape in a factory, then placed in the appropriate position on site to form loadbearing floors and walls. It also performs very well in fire and, as the supply chain develops, will compete favorably with steel and concrete on price.
Europe and Australia have made impressive starts with the new technology. Sweden, Germany, the United Kingdom, and Australia all have cross-laminated timber buildings of seven stories or more, each with a successful prefabrication story. The structure of an eight-floor building in Bad Aibling, Germany, took only three weeks to complete. London’s nine-story Stadthaus apartment building took 23 weeks less than a comparable standard concrete project.
Stadthaus provides an interesting example of innovation facilitated by carbon reduction legislation. Australian industry observers expect to see more towers such as Melbourne’s Forte in the coming years thanks to the country’s carbon tax legislation.
Sweden, Germany, the United Kingdom, and Australia all have cross-laminated timber buildings of seven stories or more, each with a successful prefabrication story
No new timber in timber land
In my hometown of Seattle, a timber town since pioneer days, the opportunities for wood are particularly exciting. I have spent the past few years visiting with designers, developers, and city officials to make the case that, with the right leadership, Seattle could become a leader in sustainable wood construction.
One local building that has gained attention for its impressive wood story is the Bullitt Center. The commercial project’s bid for recognition by the Living Building Challenge, arguably the world’s most rigorous environmental rating system, has been one of the most talked-about design stories in the city (and beyond) for several years. The six-story structure, which aims to be the first commercial Living Building in the world, employs strategies such as photovoltaics, energy-efficient windows, rainwater collection and treatment, and a materials red-list to achieve self-sufficiency in energy, waste, and water. Scheduled to open soon, it will be occupied by companies working in the green building field.
The Bullitt Center’s design includes Seattle’s first heavy timber structural system since the 1930s, using almost identical construction methods to that employed in the early 20th century. The project team also worked to ensure that all wood used in the building is Forest Stewardship Council certified, an impressive achievement for a commercial structure of this size.
However, it is my belief that future projects with similar sustainability ambitions will push wood design much further. Although 19th century heavy timber construction techniques are viable, using them to achieve environmental goals in 2013 is a bit like reducing your carbon footprint by commuting via horse and buggy. But because Seattle’s regulations for wood construction haven’t changed substantially in over a century, they proved to be the best option open to the Bullitt Center design team. The necessary testing and standardization of the new heavy timber building systems, however, is well underway.
Tentative steps in California
Another current initiative in the Bay Area holds out hope that the US will see its first significant modern mid-rise heavy timber project in the not-too-distant future. My colleague Bryce Tanner has been working with Austrian contractor Cree, which specializes in this kind of timber construction, to study what would be required to bring tall commercial heavy timber buildings to California markets. (Cree’s first heavy timber project was developed with Arup’s Berlin office.) “We’re trying to anticipate the issues that will come up and adjust the fundamental system design to overcome these problems before we start getting into negotiations with developers,” Tanner said. He and his team have spent the past few months meeting with architects, fire marshals, structural plan reviewers, and more to learn what their concerns might be and gauge interest in the system.
Most recently, the team has been in discussions with the Oakland municipal government about incorporating a heavy timber project into a masterplan for West Oakland, a former industrial zone that is one of the few undeveloped parcels of land left in the Bay Area. Several aspects of the project are exciting for the local government. First, hosting the nation’s first mid-rise wood building could bring them the public attention they desire. Second, the project could bring with it stable long-term employment opportunities. Cree “wants to teach local firms how to build in this particular way, and there are plenty of places in West Oakland where the necessary land and resources exist,” said Tanner. “They could actually set up a workshop and do the prefabrication very close to the potential building site — so that means more jobs in West Oakland.”
Barriers to implementation
Cultural prejudices are one major hurdle to widespread implementation of mid-rise wood buildings. In 2013, when steel and concrete have been the norm in tall buildings for decades, the idea of building tall structures out of wood — often perceived as dangerously flammable, insect-attracting, and decay-prone — can seem counterintuitive and even frightening. A concerted effort needs to be made to educate the public that wood can be as safe and durable for high-rise structures as conventional alternatives.
2011 Cree wood fire test
The lack of a North American supply chain also presents a significant challenge. At present, the major players in the US timber industry work solely on the manufacturing side. Effective implementation of CLT, in particular, will require the development of a unified manufacturing and fabrication process so that the wood is ready to install onsite. The potential for increasing the economic activity of rural communities is also a benefit.
There is a proven market for CLT manufacturing, and growing demand — some international projects have been delayed because the developers have had to wait to procure the material. In Europe, the manufacturing sector has been increasing rapidly over the past decade: annual production volume capacity increased from 50,000m3 to 340,000m3 in 2010. There are currently about 20 manufacturers throughout the continent, some of which are actively seeking to enter the North American market. They typically sell projects as complete systems, handling everything from panel fabrication to connection details to onsite erections.
The Canadian government and wood industry have been working to introduce CLT into the local market. North America’s first two manufacturing facilities came online (in British Columbia and Quebec, respectively) in early 2011.
And then there are the regulatory challenges. Heavy timber is currently absent from both US and Canadian building codes. Currently, designers who want to use it for a project must request permission from the relevant local authorities. The multiple jurisdictions that can come into play — local, regional, and national — further complicate the situation. (In many other parts of the world, fewer layers of regulation apply to a given project.)
In the US, the American Wood Council created task committees to begin the process of adding heavy timber to its National Design Specification (NDS) in 2011. The extensive research and testing involved takes several years; completion is not expected until late 2014. After it has been codified by NDS, heavy timber can be submitted for consideration to the International Building Code (IBC) (which, despite the name, is used primarily in the US). As the next update to the IBC after this date will not be until 2018, cross-laminated timber will not be included in US code until at least then.
One new tool that should be extremely useful for designers, developers, and others interested in implementing heavy timber is a soon-to-be-released free online handbook for the US. The handbook will make it easier to understand the relevant issues and communicate effectively with building officials.
Cross-laminated timber will not be included in US code until at least 2018
In general, Canada has been more proactive than the US in getting started with tall wood. A Canadian version of the heavy timber handbook has been available for several years from FPInnovations. In 2009, British Columbia’s provincial government passed the Wood First Act, which required wood to be considered as the primary building material in all new provincially funded buildings. The act also built on amendments to the provincial building code to allow for six-story wood-framed construction; this is expected to become a national policy. Estimates place acceptance within the national building code at 2015.
Bringing timber technologies to the US
In the long term, I’m convinced that heavy timber will be a huge architectural, environmental, and commercial success story in the United States. But there’s no reason to wait. Given the pressing need for environmental interventions, the opportunity to build more economically through prefabrication, and the potential to create new jobs in rural and industrial areas, the design community has a responsibility to ensure that this and other game-changing advances are integrated into mainstream practice as soon as possible.