Although still far from mainstream, mass timber is emerging as a more sustainable alternative to concrete and steel for constructing mid-rise buildings. An engineered product made from mature fir trees, mass timber sequesters carbon, allowing buildings constructed with it to have a carbon-negative impact on the environment.
While its sustainable qualities are attracting developers and architects, so are the speed and cost-efficiency with which mass-timber buildings can be delivered to market, noted an expert panel at the recent ULI Washington Real Estate Trends conference. Construction with mass timber can shave 30 to 90 days off a construction schedule, said panelist Steve White, principal and director of the Washington, D.C., office of Fentress Architects, a Denver-based firm.
An example is the T3 office building, a seven-story structure developed by Hines in Minneapolis and built in 12 weeks with mass-timber construction. Another project that combines mass-timber construction with concrete and steel elements, the Tallwood House at Brock Commons student residence at the University of British Columbia in Vancouver, is nearing completion. Considered the tallest mass-timber building in the world, the 18-story Tallwood House was built in less than six months.
Known also as cross-laminated timber (CLT), mass timber is an engineered wood product sold in 20- to 30-foot (6 to 9 m) panels for floors and ceilings. CLT is manufactured from small wood pieces that are glued together. (“What you have is plywood on steroids,” White said.) A companion product, glued laminated timber, or glulam, is meant for beams and columns. The technology was developed in Austria in the mid-1990s through an industry/academic partnership.
In an era of tight construction lending and rising labor costs, mass-timber projects are being delivered with greater speed and with smaller crews, the panel noted. Banks have been financing mass-timber projects, although there are too few examples to draw conclusions about their appeal with lenders or the willingness of insurers to underwrite them.
“Banks are willing to lend . . . because it holds your construction loan out for a shorter period of time, [and] you get to occupancy faster,” said panelist Jeff Spiritos, principal, Spiritos Properties, based in New York City. “Building [with] stick-frame construction, concrete, steel, with all those works, parts, and pieces, are a bigger insurance risk than mass timber is.”
Building codes across the United States, though, have not caught up with mass timber, with many either not allowing or not addressing this type of construction method. Costs associated with the materials and investment in expertise required to pull off a project are also barriers. Mid-rise projects of six to ten stories achieve optimal cost-competitiveness. Until the costs associated with mass timber come down, buildings taller than ten stories will likely continue to be fabricated from concrete and steel.
Another reason mass-timber construction has yet to take off in North America is the lack of timber engineering expertise, said panelist Jean-Marc Dubois, director of business development at Nordic Structures, a Montreal-based CLT manufacturer and developer. And engineering and design expertise is paramount. Because the buildings are created through pre-fabricated wood panels and designed with building information modeling and computer-aided design software, “you are manufacturing to millimeter-precise tolerances,” he added.
“Once the panels are cut, everything has been determined to be in the place it is going to go,” Spiritos said. “So you can take advantage of those efficiencies.”
Whereas expertise is needed to design and engineer mass-timber buildings, their assembly seems to require little experience with the product or process. One example shared by Dubois was a hotel project his firm completed for the U.S. military: the crew that built it was made up of unemployed veterans, many of whom had little or no background in construction.
A preconceived notion that mass-timber advocates are fighting is that somehow wood buildings are bad for the environment because they consume trees. Mass-timber buildings rely on sustainable forestry methods in which trees are planted, harvested, and replenished. By comparison, concrete and steel are both energy-intensive and nonrenewable resources.
“Cutting down trees is not a bad thing if they are cut down at their peak maturity with adequate carbon sequestration,” Dubois said.
Mature trees—those 20 to 25 years old—do not sequester as much carbon as do old-growth trees, but the amount is still enough to offset a percentage of the carbon emitted by a mass-timber building during its lifetime. In fact, many mass-timber buildings are considered carbon negative during the initial decades after occupancy. Stadthaus, a mid-rise residential building in London completed in 2009, stores 186 tons of carbon and will be considered carbon negative until 2029.
Buildings account for about 40 percent of carbon emissions in the United States, so advocates are hoping for wide-scale adoption of mass-timber construction methods. “We live in a time when we’re all responsible for doing no harm to the environment,” Spiritos said. “What you can do with mass timber is to reverse that degradation.”
Archana Pyati is a member of the ULI marketing and communications team.