The Lure of Mass Timber

Engineered lumber is increasingly being used for commercial projects. The result? Beautiful buildings with a lower carbon footprint than their steel-and-concrete counterparts.

We recently caught up with Boyce Thompson, who has a new book, Innovations in Mass Timber, coming out from Schiffer in May. This is Thompson’s sixth book, but his first about commercial construction.

GB: There seems to be a lot of hype/excitement around mass timber these days.

BT: Yes, and all we’re talking about is engineered lumber that home builders have used for decades. The difference is that cross-laminated timbers, laminated veneer lumber, and glue-laminated timber are finally being used on a significant scale in commercial buildings. If the market expands rapidly, home builders may suffer from supply constraints.

GB: Why are we suddenly seeing all this interest in engineered lumber?

BT:  The significant change, in the United States at least, is that the model codes allow for use of mass timber in buildings as tall as 18 stories, with graduating requirements for sprinklers and non-combustible materials. More than half the states now recognize the code change. 

It’s easy to get lost in the hype—mass timber accounts for only a tiny fraction of new commercial buildings in the U.S. Woodworks, an association that supports mass timber, only counts a little more than 2,000 commercial mass timber projects. But architects announce new ones every week that get picked up in blogs.

GB: Some of the interest undoubtedly stems from a desire to put an environmental stamp on the buildings.

BT: True. Mass timber proponents like to point out that on concrete and steel commercial buildings, the emphasis is on reducing carbon consumption after the fact, during occupancy. Mass timber offers the opportunity to reduce a building’s carbon footprint from the beginning. Wood posts, beams, and panels store carbon as long as they remain undisturbed. Some European countries view mass timber as a way to reduce carbon emission and help meet climate accords.

GB: Are the claims of sequestering carbon defensible?

BT: That’s a good question. The answer, of course, is complicated. The architects and owners of these projects plug numbers into online calculators. Input how much structural wood you plan to use, and the calculator produces numbers for carbon stored in the wood, greenhouse gases avoided, and the time taken for forests to regrow that lumber.

GB: But that’s not the whole story, is it?

BT: No. The wood must come from a sustainably managed forest, where replanted trees make up for harvested trees. Forest products companies rely on industry self-certification for sustainability claims. 

But as you know, some standards still allow for clear-cutting in giant forests. That process may result in environmental degradation, including applying herbicides, burning debris, and disturbing soil. 

The other issue is that to continue sequestering carbon wood can’t be allowed to rot at the end of a building’s useful life. Otherwise, the carbon stored in the wood returns to the atmosphere. For that reason, architects design many of the new generation of buildings for easy disassembly, something home builders might want to consider.

GB: What challenges do commercial builders face using mass timber?

BT: The industry is still working out some key details and assemblies. We’re talking about much bigger buildings than houses, which magnifies incremental costs. Considerable effort is devoted to taking costs out of metal brackets and specialty screws and bolts. 

Since wood is less dense than steel and concrete, noise transfer is a big issue, especially in multifamily buildings. Acoustic floor, wall, and ceiling assemblies remain a work in progress. 

Moisture control, something commercial developers aren’t used to dealing with on this scale, is another major issue. If mass timber expands, especially at the edges, it can halt construction.

GB: Are there other green benefits to using mass timber?

BT: Fabricators build mass timber components in factories. The pieces typically arrive sequenced and numbered for installation. That results in far fewer jobsite trips. 

Also, mass timber requires far fewer trades than concrete, which also cuts trips to the jobsite. So, you are reducing the building’s carbon footprint during construction. Moreover, contractors report that the jobsite is much quieter, a significant benefit when building in urban centers.

GB: How do the first costs of mass timber buildings compare to concrete and steel?

BT: Several building owners told me that material costs are 10 percent higher on mass timber than concrete. But when you factor in faster construction and reduced labor, it’s nearly a wash. 

Mass timber may only cost 1 percent more, though that depends on delivered prices for concrete and steel. Many early buildings leased faster than expected to big public companies interested in staking a sustainability claim. One Washington D.C. project in the book drew BP America and Wal-Mart as clients.

GB: Did biophilic interiors have anything to do with that?

BT: Owners did report that clients seem drawn to wood interiors. The few buildings that I actually walked in while researching the book had a wonderful ambiance to them, though it was tough to actually smell the wood.  

One thing to remember is that building codes restrict how much wood can be left exposed inside the building. Sometimes, it gets covered by electrical, mechanical, HVAC, and fire suppression runs.

GB: Do you buy into the science that wood interiors produce more calming, productive interiors?

BT: I’ve never worked in one of these spaces, so I don’t know firsthand. But there’s a growing body of scientific evidence that suggests this is so. One 2010 study by the University of British Columbia found that wood interiors relieve stress like exposure to nature does. 

A Brown University study found that rooms with about 45 percent wood exposure boost comfort perceptions and lower blood pressure. New studies appear regularly.

Click here to buy a copy of this book. To learn about Thompson’s other books, including Designing for Disaster, click here.