People have been gluing up wood for thousands of years. Prehistoric peoples bonded spear points and ax heads to wood with glue. The ancient Egyptians 5,500 years ago figured out how to make veneer.  Plywood is old hat: invented the year the American Civil War ended.

After World War II chemists and engineers figured out how to make synthetic glues and over the decades they were used to glue up an increasingly varied number of building materials.

These days the one getting a lot of attention is known simply by its initials — CLT.

Courtesy of New England Forestry FoundationThat stands for cross-laminated timber. It’s one of a class of what are called “mass timber” products. And there are those who follow the forest products industry who say it has the potential to reclaim some of the market share wood products have lost to steel and concrete. That could be a boon for Maine’s forest products industry.

“We think it has huge potential, which is why we’re dedicating so much of our time to it. There is the potential for sawmills to sell a whole lot more lumber,” said Russell Edgar, senior lab operations and wood composites manager at the University of Maine’s Advanced Structures and Composites Center.

In February two companies announced plans for CLT production factories in Maine. LignaCLT Maine said it plans a 300,000 square foot factory in Millinocket while Montana-based SmartLam LLC says it plans to open a $23.5 million factory at a still unselected site in the state. Both announcements said they would directly create 100 jobs, once at full capacity.

CLT is one of a class of building products lumped under the umbrella term “mass timber products.”

One of those mass timber products is glulam, short for glued laminated timber, made with dimension lumber — two-by material — stacked lengthwise and glued under pressure to make huge beams capable of bearing humongous loads. Glulam has been around for decades and is frequently used with larger buildings that emphasize open space.

CLT also uses dimension lumber, but, as the name suggests, alternates the grain of the wood with each layer — as in plywood — producing a stable panel several inches to a foot or more thick, up to ten feet wide and as long as you need. The panels are fully machined at a factory, trucked to a building site and hoisted into place by crane to form the walls, floors or roofs of a building. Often paired with glulam beams, they make for exceptionally fast construction.

CLT has been used for years in Europe, said Edgar. “In England alone it has been reported that there are over 500 CLT buildings. It is a known technology in Europe and, more recently, Canada. Like on many things we in the U.S. are a little slow to move. But I think it’s only a matter of time before it takes off in the northeastern U.S. and the rest of the country.”

Fans point out that CLT technology allows for use of spruce-fir dimension lumber, which Maine sawmills already produce in quantity. They tout its versatility: it can produce panels of virtually any size and thickness. And they note that, because wood is a renewable resource, boosting the amount of it in construction would sequester carbon, making it a more climate-friendly process as compared to steel or concrete construction.

The New England Forestry Foundation concluded in a 2017 report that there is a “significant opportunity for new CLT capacity to meet the growing demand for non-residential and multifamily housing in the northeast” and new CLT mills would have a leg up in the Boston and New York markets.

Courtesy of New England Forestry FoundationThe report also said that “New England has sufficient forest resources to support CLT plants and the region’s “sawmilling capacity is heavy to spruce/fir (50%) which is suitable for CLT.” It might be possible to use other wood species, but more research needs to be done.

The report cautioned that the CLT market is “in an early stage of development” in both Europe and North America, but could enjoy a faster growth pace than traditional wood products.

There are only five CLT plants operating in North America, the nearest to Maine is in Quebec. Only 10 percent of global CLT output comes from those plants. UM’s Edgar agrees that the “opportunity for Maine is huge and right now we think demand might only justify a mill or two, but it could eventually be three, four or five, or some of the mills might be able to significantly expand.’

Part of the problem with expanding the market for mass timber products is convincing the people who areCourtesy of New England Forestry Foundation designing buildings, and the bodies that write the building codes. The NEFF report concluded that the biggest potential for CLT is in low and mid-rise construction. In other words, multi-story apartment buildings and mid-rise office parks. According to NEFF’s report, current building codes allow the use of wood in buildings up to six stories without a variance. Anything higher than that needs one.

If a current move to change building codes for 2021 to allow for the use of mass timber products in buildings of up to 20 stories is successful, it would be a “game changer” for the industry, Edgar said.

One hurdle for CLT and other mass timber products is the perception that, because they are made of wood, they’re going to be more vulnerable in a fire than non-wood building products. That is, simply and plainly, not true, said Edgar. Scientists have studied how mass timber beams and panels perform in fire and they do quite well, thank you, with the char layer on the outside acting as a kind of shield protecting the interior, he said. It’s not going to burn like kindling.

“It’s a misperception,” he said. “It will far exceed a two-hour fire rating, as proven by recent confirmation testing. But it’s an uphill battle to get people to believe it. “It’s a challenge. The answer is in education.”

Something that might do much to show CLT’s potential and dispel myths about the product is simply to get more of them up. “We need to get up more demonstration buildings, he said. The problem with demonstration buildings is that the first one is typically slightly more expensive. “But it’s going to happen,” he said, and it will make designers and engineers more accepting of CLT as a product.

If the sweet spot for CLT is multi-story buildings, say, four to 20 stories tall, the one sector of the construction market where you shouldn’t expect it to make substantial inroads is single-family homes, said Edgar. “It all comes down to cost . . . it’s hard to beat the economics of a stick-built home,” he said. For one thing, you still have to insulate. The R-value of wood is about 1 per inch, so a four-inch thick wood panel is still going to need a lot of insulation to get it to, say, R-19.

In addition to the fire vulnerability myth, and the getting-code-acceptance challenge, another hurdle for CLT is that the nation’s forest products industry is going up against the well-heeled and influential concrete and steel industries. That is an uphill battle.

Mass timber products do have an environmental edge and these days, when a planet warming because of human civilization’s use of fossil fuels is a concern, that could count for something in the marketplace.

Wood is, after all, made of carbon. Using it in construction essentially locks up that carbon for as long as the building stands. The trees that grow to replace those harvested soak up more carbon dioxide and lock it up. “It’s geoengineering, but it’s geoengineering that we know how to do,” said R. Alec Giffen, who has synthesized the research on forests’ effects on climate for NEFF.

Those so-called substitution benefits are real, said Giffen. But they are actually not wood’s greatest environmental benefit. “The amount of wood that would be going into this stuff is not going to be revolutionary, unless we really bought into CLT” in a big way, said Giffen. Studies show that using wood in long-lasting wood products leads to far more reductions in greenhouse gases than just burning it for heat, or, in fact, just letting trees grow.

The big reason for that: making wood produces far less greenhouse gases than is emitted in the production of concrete, steel and aluminum. Giffen throws out some stats: “It takes 10 times as much energy to produce a steel stud as a wooden one” and “8 percent of carbon emissions come from the production of cement.”

Giffen said it now behooves advocates for boosting wood use in buildings to better quantify the environmental benefits by doing a life cycle analysis. NEFF is planning such a project, he said.  UMaine’s Maine Mass Timber Commercialization Center will also be conducting one, comparing an actual building design with CLT vs. concrete.

Advocates for mass timber products know that getting them to mainstream status in the building trades arena is going to take a lot more publicity and lobbying. Efforts are already underway. Check out the websites, or

“There is definitely a prejudice against wood. It’s not considered sexy and cutting edge,” said Lloyd Irland, a forest economist and the president of The Irland Group, a Maine consulting firm.

Right now CLT is used almost exclusively in showcase or boutique projects in the U.S.. IrlandCourtesy of Ken Laustsen says it’s probably too early to tell whether the market is developed enough to sustain one CLT plant in Maine, much less more. You need those “signature” or “prestige” projects to raise awareness, he said, but meanwhile, the plant needs to be able to sell its production.

However steep or long CLT’s acceptance curve is, Irland feels that “it is the one area where we have the chance at taking markets away from competing materials.” And, he said, it “provides a chance to educate a lot of people about wood and its possibilities who wouldn’t have been interested before.”



Joe Rankin writes on forestry, nature and sustainability for magazines and websites.

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