On October 23, EESI held a briefing, Wood: The Building Material of the Future?, which explored a relatively new building material to the U.S. building sector, mass timber. Unlike traditional stick-frame construction which is typically used in houses, mass timber is a class of structural wooden building materials that can be used for mid- and even high-rise construction. In addition to being a strong and safe building material, perhaps most excitingly, mass-timber products not only have a lower carbon footprint than traditional steel and cement building materials – they can provide long-term carbon storage -- turning buildings and perhaps one day, cities, into carbon sinks.
Mass Timber – A New Type of Building Material
Mass-timber is an umbrella term for a class of wood building materials. The best known example, cross-laminated timber (CLT), involves layering wood from small diameter trees or even diseased trees, to create a strong, lightweight building material. While deforestation is a pressing global concern, in the United States forest stocks have been stable for the last 100 years.
According to the U.S. Forest Service, a history of fighting forests has left domestic forests too dense and full of small-diameter trees, which act as fuel for wildfires. In California alone, the Forest Service reports that 129 million trees have died since 2010, due to a combination of drought, pest infestations and the amplifying effects of climate change. While some of these trees must be left in the forest to return important nutrients to the soil and provide habitat for wildlife, leaving millions of dry tons of wood in California’s forests would further increase wildfire risk to unacceptable levels.
Small diameter and/or diseased trees can be used to create higher value products, such as mass timber, as well as other economical uses of small diameter trees, including fiberboard, bioenergy, and other biobased products. Different species of trees can be used for mass timber, enabling manufacturers to take advantage of local wood sources.
Originally developed in Europe, mass timber made landfall in the United States around 2015, with the formation of SmartLam, headquartered in Columbia Falls, Montana. Around the same time, lumber products company D.R. Johnson, in Riddle, OR, began production of CLT, in addition to their long-standing production of glue-laminated beams (glu-lam).
Now, just a few years later, there are 13 facilities in commercial operation or in the planning stages, in eight states (AL, IL, ME, MT, OR, TN, UT, WA). International Beam’s Dothan, Alabama plant is the first manufacturing plant east of the Rocky Mountains, and expects to create 200 direct and indirect jobs in the local community. Additionally, SmartLam recently announced it will be opening a Maine manufacturing facility. On the buildings side, the projects underway or already constructed pepper the entire country.
CLT – Strong, Safe, and Sustainable
The unique properties of mass timber and CLT differentiate it from light-frame construction as they include fire safety, resistance to seismic and explosive forces, thermal performance, and aesthetics. A lightweight (about a quarter the weight of concrete) and 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.
The U.S. Forest Service, architects, and builders have been engaged with both materials testing and structural testing for CLT, and have demonstrated that CLT buildings are incredibly safe and resistant to fire, seismic and explosive forces. Currently, the International Code Council (ICC), which sets building codes, is considering 14 code changes related to mass timber. These changes to the codes deal with construction standards, performance metrics as well as fire and other safety issues for mass timber constructed tall wood buildings, which are typically buildings over 12 stories high. All 14 code change proposals were approved at the recent ICC public comment hearings, and will go to a vote with the general membership in December.
While it is generally assumed that creating long-lived wood products from sustainable forestry management activities is a carbon sink, research is ongoing to quantify exactly how much products like CLT can mitigate climate change. Understanding the scope of greenhouse gas storage from mass timber use will be important to quantify the potential of sustainable forest management activities in mitigating climate change.
Architect Susan Jones, a speaker at the EESI briefing summed up the role that forests, and forest products can play in combatting climate change. “Forests are some of our best weapons that we have in the next 5 to 10 years – to combat climate change. [We need a] virtuous circle of building, planting, building, planting. The question is which trees are you cutting down, and how are you cutting them down.”
For more information see:
- Wood: The Building Material of the Future?, EESI
- Tall Mass Timber Code Proposals Approved at International Code Council Public Comment Hearings, Building Design & Construction