Mass Timber Construction Is Evolving Rapidly

A few years ago, architects who staked an early claim on mass timber construction had to convince clients to take a chance on an exciting new approach. They would talk about faster build times and quicker leasing, sidestep the lack of comparable projects, downplay the technical challenges, and close with a statement about the environmental imperative of sequestering carbon in buildings. 

That was then. Today, owners and developers seek out architects who did the first generation of timber buildings. The architects and engineers interviewed for my new book, Innovations in Mass Timber (Schiffer Publishing), to be published in May 2024, report a growing project backlog. Woodworks, a trade association that tracks the industry, documents 18% to 20% annual growth in projects planned or completed (roughly 2,000) in the U.S. Mass timber caught on faster in Europe, which accounts for half of the worldwide volume, according to a report from Allied Market Research.

Allied forecasts 6% annual growth in the mass timber market for the next decade, but the number of new plyscrapers in the U.S. may exceed that. Many early tall timber buildings benefited from government subsidies that helped professionals work out technical kinks, including how to keep buildings dry during construction, soundproof walls and floors, limit energy consumption, and protect against earthquakes. Best practices and system details have been published for the next generation of practitioners.

The technical know-how helped the market enter a second development stage, with owners and developers pursuing market-rate projects. Some office buildings have benefited from fast lease-ups, drawing corporate tenants such as BP America, Amazon, and Walmart with sustainability goals. Universities have seized on mass timber for student housing to reduce their carbon footprint. Government entities, especially those interested in boosting a local forest-products-based economy, have turned to mass timber for public buildings, too.

Mass timber construction still faces obstacles. The buildings require extensive factory fabrication, resulting in higher front-end costs than steel and concrete. But a faster pace of construction—roughly 25% to 35% faster since trades don’t have to wait for concrete to dry—mitigates these upfront costs. Plyscrapers require fewer trades to assemble; structural components arrive at the jobsite sequenced and ready to be screwed and nailed in place. Prefabrication also cuts trips to the jobsite by as much as 80%, further reducing the building’s carbon footprint.

Early practitioners have found that project success depends on extensive pre-construction meetings, so-called “clash” meetings. Subcontractors need to agree during design where pipes, ducts, wires, and other equipment will go so that fabricators can cut pathways in the wood for the services. Subs must also agree to a predetermined work sequence, which may differ from how they’re accustomed to working.

Swatch headquarters, designed by Shigeru Ban; Biel, Switzerland. Photo via Erco.


New project sponsors often enlist the help of project and engineering consultants who have used the material before. Project teams include a timber fabricator/engineer who runs computerized stress tests, perfects joint assemblies, and consults onsite on installation. Several of the most fanciful projects in the book—FJMT’s soaring Bunjil Place and Shigeru Ban’s snakelike Swatch headquarters, for instance—owe their very existence to engineers who ran computerized tests and programmed robot-controlled saws in the factory.

Some skeptics question claims that mass timber buildings sequester carbon. They don’t dispute that trees draw and store carbon from the atmosphere. To legitimately make sequestration claims, however, the wood used to create mass timber needs to be replaced; it needs to come from a sustainably managed forest. The wood also can’t be allowed to rot at the end of the building’s useful life, or the carbon returns to the atmosphere. For that reason, architects design many of the latest tall timber buildings for easy disassembly so their wood may be used elsewhere.

Even as it evolves, the mass timber market continues to benefit from government assistance. The U.S. Forest Service, which provides grants and other forms of assistance, wants to see greater use of mass timber because it’s a way of putting to use scrub trees that might go to waste. Foreign governments, particularly those in timber-rich countries, have seized on mass timber to reduce carbon emissions and work toward meeting climate goals. They may provide development subsidies to make projects happen.

However, the market’s most significant boost, at least in the U.S., has come from new model building codes that allow for mass timber buildings as high as 18 stories. The first question asked by people unfamiliar with the science behind the code changes is, “Aren’t these buildings fire traps?” Fire testing shows that a char layer forms on the outside of glulam beams and laminated veneer lumber when subjected to fire. The char layer slows the burning process and protects the core structural section. Some evidence suggests that tall timber buildings may outperform concrete and steel buildings in fires. 

“Recent four-hour testing shows that CLT panels self-extinguish once the fire’s fuel load is exhausted in a large-scale compartment fire without sprinklers,” said Jason Wright, an architect with Hickok Cole, in Washington, D.C., which did extensive research before attempting its first mass timber project. “Fire remediators can remove mass timber’s char layer and reclad the members in wood or fireproof material. But steel will begin to yield once exposed to fire at high temperatures. It needs to be completely replaced.”

A major fire in a mass timber building, even if it spared the structure, could set back the material’s adoption. For that reason, professionals and code enforcers may err on the side of caution, doubling down on fire assemblies and limiting interior wood exposure. There’s also considerable debate within the architectural community about how tall mass timber buildings should be. Some question the added cost, lower efficiency, and reduced carbon footprint of the tallest of tall timber buildings. Eight to 10 stories seem to be the sweet spot.

My recent book would have come out two years earlier had I found enough suitable projects to profile. When I first started gathering material five years ago, it was hard to find aspirational projects, buildings with intriguing designs, the kind you see in architecture books. Early projects tended toward boxiness. Others employed decorative wood rather than structural wood posts and beams. That didn’t stop the architects from pitching the projects as “mass timber” and self-posting them as such on architecture blogs.

I also have to admit to some skepticism about the claim that exposed wood interiors produce a calmer, more productive environment, even though many studies seem to show that outcome. When exposed wood structural panels get covered by mechanicals, it’s like being in a building with exposed concrete ceilings. I also couldn’t smell much wood in the new buildings I walked through, though they were graced with distinctive interior wood details.

The mass timber market appears to be evolving quickly. In a few short years, architects, engineers, and contractors found ways to build more efficiently with mass timber. Several new off-the-shelf products, particularly in the flooring arena, have hit the market to facilitate the building method’s evolution. On the other hand, newcomers find that the projects require specialty tapes, screws, and brackets that drive up costs. Contractors may add 10% to their bids to cover contingencies. But the uniqueness and desirability of the finished building overcomes cost pressures.

“The material cost side is only part of the equation,” says Jesse Stephens of Columbia Property Trust, which developed 80 M Street, one of the first major mass timber projects in D.C. “Timber may sell at a 10% premium to steel. But if you look at the total project costs—faster construction, fewer trades, lower carrying cost—a timber building probably costs only about 1% more. I’m not a leasing guy, but having a differentiated product absolutely paid for that premium. It seems like tenants get it.”

Tim Gohkman, who developed Milwaukee’s Ascent, the tallest mass timber tower in the U.S., also managed to charge above-market apartment rents, mitigating the extra 1–2% construction charge. Noting that the building’s healthful exposed wood interiors may result in lower turnover, he speculates whether the building might produce better returns when sold one day than other buildings in his portfolio. Institutional investors may push owners and developers to use mass timber, notwithstanding the environmental benefits, if that sort of evidence begins to show up. 

Featured image: Bunjil Place, designed by FJMT, Narre Warren, Austrailia. Photo by John Gollings. 


Get smart and engaging news and commentary from architecture and design’s leading minds.

Donate to CommonEdge.org, a Not-For-Profit website dedicated to reconnecting architecture and design to the public.