The International Code Council (ICC), a trade group which sets a “model” building code followed by many cities, now lauds wood-frame buildings of up to 18 stories constructed withcross-laminated timber (CLT). That stance may surprise some people since wood has traditionally been a less sturdy and more fire-prone material, seemingly unfit for verticality. But the cross-lamination process, in which wood pieces are compressed together and treated with chemicals, makes large wooden beams and columns structurally firm and fire-resistant.
Cross-lamination also provides several cost and environmental benefits over steel frame construction. Materials are preassembled at plants, rather than onsite. That drastically cuts labor costs and carrying costs, as buildings go up faster. And because wood releases less carbon, and can capture it, the buildings are more likely to be carbon-neutral.
CLT buildings, which have long been allowed in Asia, Europe and Canada, vary widely in height. One proposed project in Japan would rise 70 stories.The tallest in America is now Portland’s eight-story Carbon12 project, although it may soon be eclipsed by a 10-story tower in Cleveland. A project in Charlottesville, Va., at eight stories, will house the headquarters of the renewable energy firm Apex Global Energy. More of these projects will surely arise as CLT production, which is now more common in Canada, becomes a staple offering of U.S. wood product firms.
But this scalability also depends on how amenable government regulators are to CLT. When the ICC voted to approve 18-story CLT construction, opposition came from the National Association of State Fire Marshals, who believe that there is not enough data to support the conclusion that CLT is safe. Individual projects have faced hurdles. The New York Times reported in 2019 that Carbon12 took two years to be approved, and CLT projects in New York City have been few, because the city has a 7-story height limit on wood buildings. The Apex tower in Charlottesville required a code amendment to proceed.
California’s 2020 statewide building code approved wood high-rises, following the lead of the ICC. Interestingly, the state fire marshal praised the change, saying that the measure could help with forest management challenges by spurring the harvesting of some trees to build CLT. However, the state only authorized CLT buildings of up to 12 stories.
But the main barrier to CLT in most cities isn’t any underlying debate about the safety of timber high-rises. It’s the fact that height itself is restricted. Most U.S. cities cap building heights even in their downtowns, not to mention the many residential neighborhoods where only single-family housing is allowed. Washington, D.C., hasforbidden high-rise buildings of more than about 14 stories in its downtown since the late 1890s, no matter what they are made of. San Diegocaps building heights at just three stories along much of its coastline; while its downtown area is height-restricted by the Federal Aviation Administration due to the nearby airport. Numerous cities, including Boston and Madison, Wis., forbid construction that risks shadowing landmarks, while Philadelphia sticks a 38-foot limit on many row houses.
So the first step to making high-rise timber construction more common is to remove the stigma — and the regulations against tall buildings overall. The second is to recognize, as the ICC has, that timber-frame towers are no more perilous than concrete or steel ones. That way maybe cross-laminated timber can become popular, and cities can enjoy the benefits of high-rise urbanism in a more environmentally friendly way.
This article featured additional reporting from Ethan Finlan.
Governing's opinion columns reflect the views of their authors and not necessarily those of Governing's editors or management.
