Wood is an attractive building material as it is a light, renewable material. Its use not only lowers carbon emissions from the building sector but also provides long-term carbon storage—turning buildings into carbon sinks. Wood’s use as a green building material has been somewhat limited in cities, as historically, wood has been used to build homes and smaller buildings, referred to as stick frame construction. However, this is poised to change due to a booming domestic wood construction sector, and recently proposed changes to the International Building Code that will allow construction of ‘tall wood’ buildings.
Mass timber is an innovative class of structural building material that could begin to transform the makeup and design of cities. Mass-timber products, such as cross-laminated timber (CLT) (dubbed “plywood on steroids”), consist of layering small diameter trees together to create a strong, safe, and sustainable building material. The unique properties of mass timber differentiate it from light-frame construction and include fire safety, resistance to seismic and explosive forces, thermal performance, and aesthetics.
Europe and Canada currently make up the majority of the global cross-laminated timber market, but the domestic market is growing due to the availability of sustainable forestry stocks and interest from building industry professionals and clients. Dozens of mass-timber buildings are in the planning or building stages around the United States, and 12 CLT facilities or processing facilities are operational or in development in eight states (AL, IL, ME, MT, OR, TN, UT, WA).
In late December, members of the International Code Council (ICC) approved 14 proposed changes to the International Building Code (IBC) that deal with mass timber, including provisions that will allow the construction of mass timber buildings up to 20 stories. The model building code (IBC) is periodically updated by the ICC, and is used as a base standard by most states, which independently develop and monitor building codes.
The changes to the building code won’t take effect until 2021, but states can independently incorporate these tall wood provisions into their codes. Already, Oregon and Washington State have allowed for the use of mass timber in buildings over six stories, and Colorado and California are also considering the change to their building codes. Interestingly, some have posited that mass-timber’s faster and cheaper construction can be a plus to crunched housing markets in California and elsewhere. Additionally, as states and the Federal Government undertake massive forest restoration and thinning projects, markets are needed for small-diameter, otherwise unmerchantable wood.
According to Mark Long, Oregon Building Codes division administrator, after the initial assessment on tall wood by the International Code Council (ICC), the state of Oregon “decided the science is done and there is no reason to wait for the ICC,” he said. “It went ahead and incorporated changes in its codes, effective 2019… Anyone who wants to build a building according to the prescriptions in the statewide alternative method can.” Long noted that these changes at the state level will have ripple effects in the mass-timber industry. According to industry research, the proposed code changes, if applied nation wide, could provide an additional 5.1 billion board feet of annual demand, mostly in the mid-rise sector (12 stories and below).
At a recent EESI briefing, speakers from the Forest Service, the forest products industry, the building sector as well as architecture, discussed why mass timber is an appealing and sustainable building material.
According to architect Susan Jones FAIA, CLT provides a lower carbon, renewable alternative to traditional building materials like steel and concrete. Healthy forests store carbon, as do materials made from wood. At the briefing, Jones, also a member of the ICC policy committee responsible for designing the new tall wood codes, noted that architects, the timber industry, fire scientists, as well as the concrete and steel industry, developed the proposed changes. According to Jones, the panel found that “yes indeed, it was safe to build tall wood buildings,” and that the 2021 International Building Code would remove several obstacles to tall wood buildings.