Housing USA: The Environmental, Speed and Cost Promise of Wood-Frame High Rises

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6 min read

Wood-frame high-rise construction may soon become commonplace in the United States. The International Code Council (ICC), which develops a model building code, recently approved mass timber construction of up to 18 floors. There is an increasing number of such structures, particularly in Europe, and several towers are being built in North America. The trend presents possible improvements to the environment, construction speed and costs of construction – assuming it does not become a target for regulators.

The emergence of high-rise wood frame buildings is enabled by cross-laminated timber (CLT), a method of gluing and compressing wood pieces together. CLT produces strong columns and beams that are designed to be used in taller buildings.

In recent months I have gotten to see a wood-frame tower up close and personal: an eight-story one in Charlottesville, VA, is arising right across the street from where I live. Begun in 2019, it will be primarily an office building that houses the headquarters for Apex Clean Energy.

But residential examples exist too: an 18-story wood frame dormitory was built in Vancouver, an eight-story condo tower has been completed in Portland, OR, a 70-story one is being envisioned in Tokyo, and other examples abound in Europe and Canada.

So, what are the benefits of wood-frame high rises? One is environmental. Wood can absorb carbon emissions, ameliorating the pollution from buildings (which now account for nearly 40 percent of emissions worldwide). One study claims that wood structure construction emits more than 24,000 fewer kilograms of CO2 than steel, over 5,000 fewer volumes of air pollutants and 90 fewer volumes of water pollutants. Another study by engineers at the University of Canterbury in New Zealand found that wood structures can capture more than 600 tons of CO2. Another environmental benefit is that the forests supplying lumber can be replanted and replenished, as opposed to the earth materials used to make concrete and steel, which are permanently extracted from the ground.

The second benefit of wood framing is speed. CLT materials are assembled after the trees are cut down, meaning that construction is prefab and takes place prior to order rather than on-site. This reduces the time needed for actual on-site work. One British project had its CLT elements built in three months with five staff members. Alan Taylor, the developer for the Charlottesville project, says CLT-framing has shaved several months off construction time.

The third benefit is cost – which is largely related to speed. Although timber frames have higher upfront costs than steel, according to Taylor, this is offset because assembly is faster and requires fewer skilled craftsmen, such as welders.

“A huge driver is your carry costs,” says Taylor, president of Charlottesville-based Riverbend Development. “We spent $3.5 million designing this [Apex] building, and you gotta carry that, then the land, then you gotta build the building, then you’ve gotta carry that, because nobody starts paying rent until they’re in the space. And so, you’ve got four to five years of carry.”

But the offsite assembly reduces this carry time and requires “three to four times” less labor, Taylor says.

Given these benefits, such projects are theoretically attractive for affordable projects, especially for firms, which want to prioritize environmental sustainability (or who are mandated to by green building codes). But the market is nascent, and developers are likely to face challenges with regulations and scaling issues.

While the ICC may have approved wood-frame high rises, that might not be enough to assuage the concern of regulators. Amid debate over the rule change, the National Association of State Fire Marshals objected on safety grounds. The organization argued that insufficient field testing had been done and expressed concern that sprinklers could not be relied upon in the event of fire.

“It is extremely difficult to accept that these proposals meet the committee’s own stated objectives. We are left with ‘professional judgment’ as the only substantiation,” a briefing found.

But proponents dispute the legitimacy of these concerns: CLT is specifically designed to be fire resistant. The structures dissipate oxygen more quickly, limiting the ability of fire to spread. And lamination is able to resist fire better than steel, according to Joseph Marchetti of Hourigan Group, the contractor on the Charlottesville project. Non-laminated stick frame timber, by contrast, burns more quickly.

Of course, field testing has been done for mid-rise CLT contexts. A 2000 British study, conducted in a six-story wood tower, found that the building performed, as well as non-wooden structures of comparable height against fires, but living rooms fared somewhat worse in wooden structures than otherwise. It flagged windows as vulnerable to causing flames to spread between floors. The test results prompted a change in Canadian building codes.

Legitimate or not, such safety concerns will surely feature prominently in zoning decisions and on a project-by-project basis. The Charlottesville project required an amendment to the city’s code and was only allowed to build six of its floors with wood, out of safety concerns (though the lower floors were built for parking, leading to additional weight considerations).

But in the near term, the bigger issue may be scalability. While European markets are competitive, because such construction is more common there, CLT is less common in the U.S. There are some firms in Canada and the Pacific Northwest that make it, but not a lot. The CLT used for the Charlottesville project was from Nordic Structure, a company in Montreal.

A potential further complication comes in the form of the tariffs that U.S. regulators have imposed on Canadian wood in recent years. (The tariffs were reduced, drawing praise from the National Association of Home Builders). It’s unclear how much the lumber-focused rules apply to the treated and pre-manufactured timber used to make CLT, but the recent regulatory disputes may give the industry pause.

If scalability can be achieved, and regulators can be convinced that CLT delivers safety benefits that its promoters tout, high-rise wood-frame construction could become more prominent in years to come. The benefit of pre-manufactured material seems poised to benefit affordable projects, while the carbon capture angle could prove favorable for cities, which are aggressively pursuing energy-efficient construction. Expect to see more such developments.

This article featured additional reporting from Market Urbanism Report content staffer Ethan Finlan.