Mjosa Tower in Brumunddal, Norway. Anti Hamar
Nearly thirty years after the peak of the Timber Wars, when Earth First! and other environmentalists protested widespread logging in Oregon and Northern California, it seems almost counterintuitive that wood is now considered a sustainable alternative to concrete and steel construction.
But recently mass timber, an engineered wood whose compressed layers are glued or nailed together into various structurally resilient components such as beams, panels, and columns, has become a growing force in the United States. (The most common form of mass timber used for building is cross-laminated timber, or CLT.) According to mass timber proponents, CLT use will significantly combat greenhouse gasses and, in turn, global warming. As a natural and renewable resource, mass timber promises to minimize excessive emissions associated with standard construction. It also naturally traps carbon, preventing its slow release into the atmosphere.
Already an established movement in Europe, mass timber construction continues accelerating in North America, particularly in the Pacific Northwest and British Columbia. In 2018, the Timber Innovation Act passed legislation as part of the Farm Bill, sparking more interest in wood construction.
Until recently, mass timber projects have been limited in scale, but high-rise wooden buildings may soon be dotting the skylines across the country. In downtown Milwaukee, the Ascent MKE, a 25-story hybrid timber apartment tower currently under construction, is the tallest CLT structure in the world, and designs are in the planning stages for projects from Philadelphia to Chicago to San Francisco.
Ascent Tower in Milwaukee, Wisconsin. Stacey Wescott/Chicago Tribune
Aside from its environmental friendliness, mass timber has attracted developers for its economic benefits. By using prefabricated wood, developers benefit from lower costs and, more important, perhaps, from much faster completion times. And because the components are manufactured elsewhere, mass timber construction sites are smaller, cleaner, and cheaper. "Aside from all the performance advantages of mass timber, some of the biggest benefits come from the ability to pre-plan and prefabricate mass timber buildings," Nate Bergen, project development manager at Kinsol Timber Systems, told The Daily Hive. "We go from digitally pre-planning our work, prefabricating the different parts of the building to constructing on-site. People who are new to building with mass timber are often astonished to see the building elements arrive on-site and pretty quickly the building is going up."
In some ways, this is a back-to-the-future moment, reminiscent of the modular innovations of the mid-1800s, when precast iron kits were shipped to New York City to develop the now-iconic SOHO neighborhood and when manufacturers supplied boomtowns in the West with prefabricated lumber. Years later, the E.F Hodgson Company sold modular homes via catalog, a practice successfully adopted by Sears & Roebuck. The difference today, of course, is that the use of CLT is predicated on sustainability.
Estimates of the impact new construction has on the environment vary, but the conclusions are clear: the building industry contributes to air pollution, fossil fuel burning, and the exploitation of natural resources. Mass timber production requires far less energy than that necessary to manufacture a comparative amount of steel. Similarly, mixing concrete (standard material for mid-rise buildings in the United States) releases excessive greenhouse gasses that, by some measures, account for 4-8% of the carbon emissions in the world. This is an environmental hazard that mass timber sidesteps entirely.
In addition to environmental benefits, mass timber construction could also be a boon to local economies, possibly reviving dormant sawmills and the long-stagnant logging industry. At the same time, more mass timber projects might mitigate some of the rampaging fires recently seen on the West Coast. The Timber Wars of the 1990s were so successful that harvesting has declined more than seventy percent in California from federal restrictions imposed decades ago. This may have had serious collateral damage in the form of accelerating wildfires in overcrowded forests. "When John Muir arrived and discovered Yosemite, we had about 40 trees to an acre. Today we have hundreds of trees to an acre," Rich Gordon, president of the California Forestry Association, told Reuters. "We will be better off if we can get closer to the way our forests once were."
Finally, the aesthetic appeal of mass timber is also undeniable. Exposed wood offers interiors a rich, vibrant warmth and gives facades a unique look in an era when so many new buildings are variations on glass and steel grids.
With its low environmental impact, potential to offset carbon emissions, and relatively simple assembly, mass timber seems like the perfect alternative to steel and concrete. But there are still some questions surrounding large-scale mass timber construction. Among these questions are concerns over fire performance and the effect of ramped-up manufacturing on the environment because while wood is a renewable resource, it is also one that takes time to replenish.
The key to wider acceptance of mass timber is responsibly-sourced wood from certified harvesters. "We must ensure that mass timber drives sustainable forestry management, otherwise all of these benefits are lost," Mark Wishnie, director of forestry and wood products at The Nature Conservancy, told Yale Environment 360. "To really understand the potential impact of the increased use of mass timber on climate we need to conduct a much more detailed set of analyses."
As far as safety is concerned, research and testing have determined that when timber is exposed to flame, it will char, delaying the spread of fire. "Due to its plywood-like layers, cross-laminated timber, or CLT, has been found to char during a fire at a slow enough rate that it can take more than 90 minutes of burning for a structure to collapse," reported Fast Company. "By comparison, tests done on single-story wood-frame homes resulted in collapse after just 17 minutes." Although test results have been promising, research regarding mass timber and high-rises is ongoing. But, as with many innovations designed to combat climate change, mass timber construction is not a cure-all. As a partial solution to the environmental challenges facing us, however, even its seemingly paradoxical genesis seems mild. "Cutting down a tree is something we were told at a very young age is bad," Peggi Clouston, professor of Wood Mechanics and Timber Engineering at the University of Massachusetts at Amherst, told the Washington Post in 2019. "But it's not true. Think of the future population and how are we going to house them. If we continue building solely in concrete and steel, we won't have a planet to put people on."