How CLT could change the US building landscape
Project teams looking for building materials and systems with a lower environmental impact are increasingly eyeing wood — specifically cross-laminated timber (CLT), a type of mass timber that, research has shown, rivals concrete and steel in performance but has a smaller environmental footprint.
Still, supply-side challenges have made it hard for mass-timber products to gain a foothold in the U.S. market. Mill owners have proven generally unwilling to update their production lines to make large CLT panels until there is a steady demand, but demand won’t pick up until material prices come down and local codes become more accepting of the new material. And that’s not likely to happen until supply increases, and with it the number of real-world projects.
At the Urban Land Institute’s Washington Real Estate Trends Conference, held in Washington, DC, on April 25, distributors, developers and architects shared their views on the future of mass timber for construction.
CLT could gain acceptance in the U.S.
While CLT has been used in buildings across the globe, U.S. markets have been slower to adopt it for structural applications, especially in high-rise buildings. Already, CLT projects in the U.K., such as Stadthaus, in London; Bergen, Norway’s Treet; and Vancouver, British Columbia, Canada’s Brock Commons, which is currently the tallest mass-timber structure in the world; stand nine stories or higher — two stories more than the tallest mass-timber building in the U.S.
Europe is already home to a number of mass-timber high-rises that stand taller than six stories, and several others are currently in progress, according to Steve White, principal and director of Washington, DC–based Fentress Architects. Still, the U.S. lags Canada and some European countries in its use of structural CLT. That’s in part due to difficulties reconciling local building codes with CLT’s properties, said Jean-Marc Dubois, director of business development for distributor Nordic Structures.
The International Building Code has been slow to recognize CLT as a structural construction material. What’s more, a proposal to raise the maximum height for a CLT high-rise from six to nine stories was shot down in 2015, ahead of changes to the 2018 code update.
Still, industry members are optimistic. New York City–based Spiritos Properties Principal Jeff Spiritos predicted that CLT will be the dominant structural system in the U.S. for four- to 12-story buildings in the next five to 10 years.
"As there are more and more manufacturers, as there is more and more technology that’s built into the system, and as the mass-timber products become more durable and more cost-effective, it’s even going to rival stick-frame construction," he said.
Mass timber will be environmentally imperative
Critics argue that using timber en masse could lead to heavy deforestation in the U.S. Dubois disagrees. According to figures by the U.S. Department of Agriculture, net annual North American forest growth accounted for 26.4 million cubic feet in 2011. Forest removal for the period, in contrast, was 12.8 million cubic feet. More still, the total volume of trees growing in U.S. forests has increased by 50% since the 1950s, according to the 2010 U.S. Forest Service Resources Planning Act Assessment.
A 2009 study by engineering researchers at the University of Canterbury, in New Zealand, found that a mid-rise steel or concrete building can produce up to 1,500 tons of carbon dioxide emissions. An equivalent mass-timber building, in contrast, can sequester 610 tons of net CO2 emissions. Mass timber curbs emissions by storing CO2 in the harvested wood — the material, in turn, passively reduces carbon in the environment when it is used in place of energy-intensive materials like steel and concrete.
London’s Stadthaus residential building goes beyond carbon-neutral to be carbon-negative. For the first two decades of its life, the structure will offset CO2 emissions equal to those generated in its development before becoming neutral in offsetting global greenhouse gas production.
"Forty- to 50% of greenhouse gases come from extracting and producing the building materials we use," Dubois said. "What you can do with mass timber is reverse that degradation [and] environmental upheaval."
CLT could ease pressures from labor shortage, rising business costs
The use of CLT could help offset the strain of the continuing skilled-labor shortage. Spiritos research found that using mass timber compared to traditional building materials resulted in a 20% faster construction schedule, on average. Brock Commons, for example, saw its 17 wood floors (above the ground-level podium) go up in just nine weeks with a six-person crew for its CLT installation.
CLT construction can be less time-intensive because the material arrives to the job site pre-cut, with the panels and even entire floors ready to go. That allows workers to reduce the risk of error and get the assembly process underway quickly.
According to White, mass timber could be the sweet spot for developers looking to optimize their labor pool, costs, project schedule and foundation work. Still, it’s unclear yet whether CLT will be definitively less expensive from purchase to installation and even once the building is in use, and whether the payoff will be worth the added time spent researching and developing ways to make the product work.
Mass-timber advocates tout wood’s lower weight relative to concrete and steel as another benefit to using the material. Lighter-weight materials can lead to significant cost savings on foundation work. With material price increases being one of this year's most leading concerns among the industry, the development of a more cost-effective alternative to traditional building materials could be key to helping advance adoption.
Building code updates, initiatives could boost CLT's stake in the industry
Though the next set of updates to the International Building Code will be released in 2018, additions to the code that could stand to alter CLT's foothold across the U.S. likely won’t come until 2021. In January 2016, the International Code Council, which governs the IBC, voted to create a committee that would study high-rise timber projects, test applications and could propose updates ahead of the 2021 revision.
Should they happen, such updates could prompt more municipalities to incorporate mass timber into their codes and developers to consider the material for projects in the U.S. Even without updates to the IBC, developers across the country are embracing CLT with performance-based code exceptions, especially for height. At seven stories and 220,000 square feet, Minneapolis' T3 is the country's first modern mass-timber building. T3 crews framed 180,000 square feet in just over nine weeks, averaging around 30,000 square feet of floor space per week. Meanwhile, the University of Massachusetts at Amherst recently opened a four-story, 87,000-square-foot engineered wood building.
Incentives to use CLT and other mass-timber products could help the material gain traction in the U.S. market. In 2015, the U.S. Department of Agriculture encouraged the use of wood in construction by sponsoring the Tall Wood Building Competition. The two winning teams, one from Portland, OR, and one from New York City, were given $1.5 million each to help develop their winning engineered-wood designs. Portland’s will stand 12 stories tall and feature retail, office space, workforce housing and public areas. In New York City, what would have been a 10-story mass timber condominium building in the city’s Chelsea neighborhood was canceled after its developer said lenders indicated little interest in supporting the project as growth in the high-end multifamily market there slowed considerably since the planning stages.
Although CLT promises much in the way of cost and time savings and a smaller environmental footprint, developers must do their own due diligence to determine if the material is right for their projects.
"The way forward is to commit to a timber research effort, design your buildings schematically and them price them out," Spiritos said. "Mass timber is the optimal and perhaps only building system that can reduce the cost and simultaneously improve the quality of your project."
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