Is Mass Timber The Path To Sustainable Construction?

As people become increasingly interested in the sustainability in all things, building construction was bound to find itself under scrutiny. Steel and concrete are notorious for their large environmental footprints. But they’ve historically been the only suitable answer as the primary load-bearing material for large, and especially tall, buildings.

That may be changing. Mass timber – engineered wood members  used as structural components for buildings – is getting a lot of attention lately. “Mass timber is very exciting. It’s a long-term durable product. It’s a critical carbon storage tool,” said Mark Rudnicki, Ph.D., Professor of Practice for Forest Biomaterials at Michigan Technological University and Executive Director for the Michigan Forest Biomaterials Institute. “Plus, it’s cost-effective, and aesthetically pleasing.”

The carbon storage element is a big part of the new interest in mass timber. The production of steel or concrete emits large quantities of carbon dioxide (CO2). Wood is produced naturally when trees grow, and they “inhale” CO2 in the process, chemically locking it away. So long as the wood doesn’t rot or burn, the CO2 stays locked away. Using wood as a building material keeps the carbon captured until the building is destroyed and the wood degrades. A 2014 study published in the Journal of Sustainable Forestry calculated that a 14% to 31% reduction in global CO2 emissions could be realized by substituting wood for concrete and steel in building and bridge construction.

There are a number of different types of mass timber, distinguished by assembly and joining methods. The most popular recent development in mass timber is cross-laminated timber (CLT), in which pieces of wood are joined with adhesive in a staggered pattern in which each piece is at right angles to the next, imparting greater strength to the finished member product. One producer of CLT is SmartLam North America, which was reorganized in 2019 to support the growing mass timber market in North America. The company is an expansion of SmartLam, a company that has been an industry leader in CLT since its inception in 2012 as the first U.S. manufacturer of CLT. SmartLam North America is headquartered in Columbia Falls, Montana. The company announced in October that it had acquired the former IB XLam facility in Dothan, Alabama, increasing its annual CLT production capacity to six million cubic feet.

“CLT forms a monolithic block of wood that can be used in place of steel and concrete,” said Casey Malmquist, SmartLam North America’s Chief Strategy Officer and co-founder. “Typical uses of mass timber would be for beams and columns using glue laminated timbers, and CLT as a replacement for a poured concrete floor systems. It has better thermal properties than steel or concrete. Plus it’s better in seismic conditions – it has a ductility. The strength of a tree isn’t in its rigidity, but its flexibility. It maintains its strength despite movement.”

Mass timber offers construction advantages too. “It pushes people offsite,” Malmquist explained. “You can make ‘Lego pieces’ in the shop, milled pieces that form specific parts of the building. For example, we had a job in Tacoma and because of what we do offsite, eight people were able to deliver the same results it would have taken 50 people to do onsite with conventional construction methods. It’s much faster, too, so you can get the building up and dried in more quickly.” 

SmartLam North America, predicting a coming boom in mass timber construction, has plans to expand to other areas of the country. “We’ve got plans to move into the other ‘wood baskets’ in North America,” said Malmquist. “We’re looking at the whole southern U.S., the Northeast, and the West coast. That would help us reduce shipping costs, by putting us closer to the largest marketplaces.”

There are still hurdles to overcome, though. Building codes evolved to make wood construction of large buildings difficult, after large-scale urban fires like those in Chicago and San Francisco in the 19th century, which were fed by “stick frame” wooden buildings. Mass timber behaves differently. “We did extensive fire testing,” said Malmquist. “Mass timber has a charring effect and is self-extinguishing. Try lighting a log on fire . Meanwhile, concrete becomes brittle and steel fails.” Rudnicki agreed. “Fire prevention research and design are a big part of making mass timber more feasible,” he said. “The thing is, mass timber is thick. It burns slowly and predictably, and commonly puts itself out. It can be engineered to last through a fire, with designs to have it last two or three hours so people can get out and the fire can be extinguished.”

Different types of wood create another opportunity. “What I’d like to see is the use of local timber,” said Rudnicki. “That poses a challenge, because many states have mostly hardwood species. CLT right now is made with softwoods such as pine, spruce and Douglas fir. At Michigan Tech right now we’re exploring using different hardwoods like maple, ash and oak, and CLT panels that are a mix of hardwood and softwood like maples and white spruces. Other schools are working on hardwood CLT too. Virginia Tech, for example, is working with tulip poplar, a lighter hardwood.”

Cost is another factor. “Hardwood as a rule is more expensive,” Rudnicki said. “I could see things changing to where hardwood is only put on the outside of mass timber, for both aesthetic reasons and durability advantages. I expect that eventually there will be a wide variety of wood combinations depending on customer, application and local availability. Patterns of wood use are changing, with the decline of magazines and newspapers. Ugly hardwood that goes to the pulp mill now for paper could be used as an inner layer of mass timber. It’s still strong, and nobody will care what it looks like.”

Mass timber should continue to get a boost as people look more and more toward reducing CO2 emissions. “We need to change people’s attitudes about forest management,” said Rudnicki. “It’s okay to cut a tree. If you don’t use our forests, you’re choosing oil. There’s still a stigma there from our history before sustainable forest management, and from what’s going on in other parts of the world today, that we have to overcome.”

Malmquist agreed. “In a nutshell, this is a proven sustainable model for building,” he said. “Wood is our only renewable building resource.”