By Brent Sohngen
The Ohio State University

A material that’s been around since people built shelters – wood – is increasingly being proposed for low- and mid-rise buildings.

Companies behind these mass timber projects say that wood is a lower-carbon alternative to steel or concrete and brings other benefits, such as faster construction time and lower cost than concrete and steel. Advocates say the wood materials, made of compressed layers of wood with glue, offer good fire safety as well.

The work forests do

One way that researchers assess the environmental footprint of a product or service is called a life-cycle analysis, which calculates the cradle-to-grave impact.

One life-cycle analysis found that using mass timber in a 12-story building in Oregon had an 18 percent lower global warming impact compared with constructing the building with steel-reinforced concrete. The carbon emissions benefits are even greater when comparing timber with steel for low- and mid-rise buildings.

In these studies, the global warming benefits mostly result from lower emissions in sourcing, transporting and manufacturing the material for these large wood buildings, compared with steel or concrete components, rather than efficiencies in heating or cooling or disposal of the materials at the end of the building’s lifespan.

On a global level, the raw material for mass timber – forests – absorb large amounts of carbon dioxide from the atmosphere, making them an important carbon “sink.”

Tree cutting is one of the most widespread disturbances in forests, yet, after accounting for all harvesting, fires, land use change and other disturbances, forests in the United States still remove a net 754 million tons of CO2 per year from the atmosphere, an amount equivalent to 13.5 percent of U.S. emissions. Globally, the picture is similar, with forest growth removing 2.6 billion tons of CO2 more from the atmosphere than the combined effect of all wood harvesting, deforestation, forest fires and other disturbances.

Although today forests are a net CO2 sink in the U.S. – taking in more carbon from the atmosphere than released through disturbance – before the middle of the last century, they were a big source of carbon emissions. Back then, farmers converted land to agriculture, foresters cut old-growth trees to produce lumber and forest fires raged.

Carbon losses in the U.S. were so large that land-based emissions around the turn of the 20th century were on par with emissions from deforestation in tropical regions today.

Over the past 100 years, the trend has reversed, as forests have removed far more CO2 from the atmosphere than they have released. One reason for this transition has been a sustained increase in crop yields, which has allowed for greater farm output on fewer acres. As a result, grain prices fell in real terms and farmers abandoned less productive lands, allowing forests to return. These regrowing forests, in turn, removed carbon from the atmosphere.

Abandonment was not the only reason trees regrew in the U.S. Even as foresters were still sawing their way through old-growth stocks in the first half of the 1900s, some foresighted forest landowners began planting trees because timber scarcity was growing, as evidenced by timber prices rising at 3 to 4 percent per year. By the 1950s and 1960s, over 1 million acres were being planted annually in the U.S.; today, the area planted is double that.

Economics of forest management

To examine whether wood is sustainably sourced, rather than contributing to higher carbon emissions, it is instructive to consider the economics of forest management.
A shift toward using wood rather than other materials in low- to mid-rise building designs will drive demand for wood products, resulting in both more harvesting and more planting. Any increase in harvesting carries risk, including an increase in carbon emissions, habitat loss and other impacts. Perhaps the most evident effects happen when surging demand causes logging in sensitive ecosystems, critical habitats or old-growth forests. If lost, ecosystem services like biodiversity are often impossible to replace.

Carbon may be less of a worry because it can be returned to forests through regrowth. However, some critics maintain that harvests deposit CO2 in the atmosphere for the period between a timber harvest and forest regrowth, resulting in a massive CO2 emission.

There is considerable debate about this “excess” emissions hypothesis. Other research into the effects of increased wood demand illustrates that both harvesting and regeneration increase when demand rises. When timber investments are modeled alongside harvesting, carbon stocks in forested lands increase when wood demand ratchets up. This finding is not new. The example of the last century reveals that elevated timber demand and higher wood product prices strengthen incentives for landowners to intensively manage commercial forests – plant more acres, improve varieties, shift species mixes, fertilize, control drainage and manage competition.

The sustainability of mass timber will also be determined by which forests supply this new demand. It is unlikely that much of this new harvesting will happen on the 42 percent of U.S. forests owned by various units of government. Many of these forests are either administratively protected – for example, as a wilderness area – or are remote and costly to access. Where cutting is allowed, logging is slowed by the considerable planning, impact assessment and public involvement required.

Even many private landowners have gotten into the habit of protecting for the purpose of environmental services. Today, over 37 million acres of private land in the U.S. are enrolled in conservation easements, which limit what current and future owners can do with their land. Not all of these protected lands are forests, but where they are, new demands for mass timber are unlikely to result in more harvesting.

Aside from these legally protected lands, forest protection happens in many private forests simply because many forest owners are inattentive or they have strong preferences for wildlife and benefits other than timber revenue. As a result, research has found that nonindustrial landowners as a whole are unlikely to expand cutting even if demand does grow substantively.

Role of planted commercial forests

At the other end of the spectrum, industrial interests own just 20 percent of U.S. forests, but supply 46 percent of the nation’s timber. An overwhelming share of these forests are managed intensively with plantations. Tree planting is so prevalent that industrial owners account for 60 percent of private planted forests, defined as those that are artificially regenerated via planting or seeding.

Intensive management explains how so few industrial forests can support such expansive harvesting. If demand rises, these owners will have strong incentives to increase harvests. Yet because forests are a valued asset, they will also grow more and bigger trees with new plantings and intensified management.

One effect of climate change on forestry is that rising carbon dioxide levels have increased forest growth through higher rates of photosynthesis. A 2022 study found that elevated levels of CO2 had a particularly large effect on wood volume in younger, planted stands. Not only did forest plantations contain more wood volume at the same age than natural stands, but the study estimated that over the past 50 years, planted stands gained 62 percent more volume from this carbon “fertilization.” The number of trees per acre did not change substantively over this same time period, so most of this wood volume increase resulted in bigger trees.

Between 1997 and 2017, industrial owners accounted for eight out of every 10 new hectares of planted forests on private land as they doubled plantation area. No one will confuse these forests for old-growth forests, but from a commercial perspective, planted trees have become the lowest cost source of timber. They also relieve pressure on natural stands.

More critically for the atmosphere, expanding the area of young, fast-growing stands enhances the overall carbon sink of forests and brings an incentive to manage forests that serve the built environment.

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Ben Kaiser, owner and principal of Kaiser Group + Path Architecture, believes the building industry can play a big role in reducing carbon emissions and combating global climate change by adopting mass-timber construction. So the multidisciplinary firm behind Carbon12, an eight-story mixed-use building in North/Northeast Portland that remains the tallest one in the U.S. made of mass timber, has decided to share its knowledge and experience.

Kaiser + Path is making available online all drawings, technical specifications and engineering documents related to Carbon12 at .

The obvious question is why?

“Sometimes I ask myself the same question,” Kaiser said. “It’s interesting because it’s such a new world, the world of mass timber, that we’d like more people to join us in the undertaking. We’re convinced it’s the correct path forward for the environment, but just us doing it by ourselves in Portland is not going to make that big of an impact. So we really feel the more people who can come and join us and build momentum, the better it will be for the environment and the timber industry in the Northwest.”

Portland firm Hacker is another early adopter of mass-timber construction, and recently moved into its new headquarters in District Office – a six-story, mass-timber office building in the Buckman neighborhood. Corey Martin, a Hacker principal, said he’s not particularly surprised by the decision by Kaiser + Path to release project documents.

“The mass timber movement is bringing together people and professionals in our world in ways that other things haven’t,” Martin said, “because the innovation and change in what’s possible is literally changing every minute as we work in real time. There’s a lot of mutual benefit for us to share. It’s like an open-source community that we have, so it’s fitting in with that.”

Carbon12, completed in 2018, took the industry by storm and generated substantial press for Kaiser + Path. The project team worked with city and state officials to circumvent restrictive codes limiting heights of wood buildings. Carbon12, at 85 feet, became the tallest building in the country with cross-laminated timber, glulam beams and columns, and other mass-timber elements.

“We were blown away by all the ways mass timber keeps improving the conversations,” Kaiser said. “We were glad we broke through the 65-foot height limit for wood; we now have a new precedent of 85 feet, and that was a big change for the United States.”

The project team knew it was the right path forward, Kaiser said. But additional benefits were found along the way. The project turned into a proving ground for mass timber, thanks to structural testing requirements pushed by the city and state.

“We kept discovering great things about the mass-timber products,” he said. “These are far superior in seismic events. These buildings are just 30 percent the weight of a concrete building, and you can imagine as you go higher, 70 percent less mass is a lot easier to restrain with regard to lateral forces.”

Mass-timber buildings also impact the foundation less, allowing their use on formerly polluted sites or brownfield sites.

“Carbon sequestration is why we got into it,” Kaiser said. “But the modularity, seismic superiority and the aesthetics all kept improving the conversation for us.”

Taylor Cabot, now a Swinerton Mass Timber project manager, served in that role for Kaiser + Path during the Carbon12 project.

“(Carbon 12) was built before codes, so we went pretty much where we wanted to go with it,” she said during a recent Women in Construction Week event. “There was no code path forward, and the city said, ‘This is beyond our scope.’”

The state of Oregon, however, provided more regulatory framework. The Oregon Building Codes Division was in the process of creating a method for reviewing cross-laminated-timber buildings for local jurisdictions and wound up collaborating with the city of Portland’s structural engineer, fire marshal and life-safety reviewer.

The result was a unique review process wherein the city was responsible for aspects of the building outside of the physical structure, while the state reviewed structural and fire and life safety elements.

“The good news is we took a pretty prescriptive path,” Cabot said. “It really allowed us to hear rumors or feel the feel of people getting nervous about what they were seeing and immediately addressing them. We’re still building a lot of buildings in Type III, but we will all be moving very quickly to Type IV, which has a lot of advantages and will speed up the process. I’m excited because this will allow projects to move through the permitting process a lot faster.”

The stream of industry inquiries and requests for information about Carbon12 also played a role in the decision to open it up for examination. Kaiser estimated the firm has given more than 200 tours of the building.

“That’s the exciting thing,” he said. “We’ve joined a like-minded community of folks internationally. If we were doing strip malls in Phoenix, no one would be calling us. But since we’re doing something innovative and exciting, we’re getting calls and visits from people around the world. That’s one of the nicest outcomes we hadn’t planned for.”

Martin wholeheartedly agrees.

“We all share the same consultants, the same engineers – there’s a lot of cross-pollination there,” he said. “Structural systems weren’t a thing we all looked at as a point of innovation for a long time in normal projects. But now, the structural system is this big question mark and this big point of conversation, so it’s really fun. That’s why we’re all wanting to share stuff.”

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“You’re standing on the tallest wood building in the United States,” said Ben Kaiser on top of his Carbon12 at North Williams Avenue and Northeast Fremont Street.

For the moment, he’s right. It’s also the first residential use of timber framing at its height in the U.S.

At 95 feet and eight stories, Carbon12 is a shade taller than architect ; the Minneapolis structure held the distinction for only a few months.

T3 and Carbon12 both employ mass timber in their structural systems – T3 with nail- and glue-laminated timber and Carbon12 with a hybrid of cross-laminated timber (CLT) and a steel core. Both were asked to compete in the USDA’s , though neither won. A different Portland wood skyscraper, the Framework tower, ended up splitting the $3 million prize with a now-scrapped New York City project.

The design competition, backed by the Obama administration, evidently helped invigorate the race to erect so-called wood skyscrapers in the U.S., a contest Portland is well-positioned to dominate.

Building codes in the U.S. for more than a century have discouraged use of wood framing in structures taller than five stories because of life safety concerns. CLT, however, especially in concert with other forms of mass timber, have the potential to change this. They’ve already been in use elsewhere – notably Europe and Canada – since the 1990s.

PATH forward

Kaiser, head of development firm Kaiser Group and design-build firm PATH Architecture, to many people represents the human face of gentrification in rapidly changing Northeast Portland. Heavy on sustainable features, PATH projects are described as the epitome of green building methods, sleek design and low environmental impact.

Kaiser wants Carbon12 to be a continuation – visually and thematically – of his One North mixed-use office project kitty-corner across the street. (The other half of the Carbon12 lot is planned to contain a 65-unit aging-in-place concept called The Canyons.)

The CLT panels were delivered to the site in 22 flatbed trucks with brackets and other attachments already installed, meaning the panels only had to be fitted into place with the tower crane. The crane itself was only on-site for two and a half months.

Carbon12 will have two units per floor. Recesses in the east and west sides of the building will have ivy running up them, as high as it will grow. Kaiser, a registered architect, was inspired by the concept of a “nurse log” – a fallen tree that then nurtures other life.

“Once a tree falls, it’s only lived about half its life,” he said. “It gives those nutrients to the next generations. It’s a fantastic way to think about architecture, especially at this moment with the advent of CLT.”

Though the building flaunts its wood, it actually employs all of the big three building materials. Steel is used in the core and braces that connect floor plates to the vertical columns. And concrete is used on the basement, ground floor and garage. (The automated garage represents another first for the U.S. The German-designed underground system will deliver drivers their vehicles without them ever needing to venture below-ground.)

Kaiser said it’s wrong to think of building materials in competitive terms, as some unions and industry groups have done.

“I really think everyone should just relax and let the products perform where they perform best,” he said. “There’s plenty of market for everybody, and I think that we all need to work together to make each other better, rather than trying to out-prove one another,” he said.

Kaiser received an undisclosed amount from the Softwood Lumber Board to help test aspects of his project. He said he and his firm will only build with mass timber from now on. He thinks one day the skyline of Portland will be dominated by wood.

“This is our way forward, and we’ll keep applying what we’ve learned,” he said.

Knocks on wood

The Framework team plans to celebrate the award of building permits from the state and the city later this month. But it has already notched many milestones. The project has won design review approval, and concept testing – fire, acoustic, seismic – has been carried out at laboratories around the country.

The team now is looking ahead to a 14-month construction schedule, starting in late summer.

“The piece we’re looking at now is the financing,” said Anyeley Hallova, a principal with project^. “It’s a complex project of affordable housing in it, market-rate office. It will take a little while now to put that all together.”

But Framework’s East Coast counterpart hasn’t had the same good fortune.

The ownership group split several months ago when it became clear the New York Fire Department remains reluctant to adopt mass-timber performance, according to sources close to the project. And the New York Building Department is still following the 2012 International Building Code, not the 2015 one, which is said to be more favorable to CLT.

“They’ve been reluctant to engage with developers who are willing to do performance-based approval,” said Jeff Spiritos, principal of Spiritos Properties. He said his business has moved on to working on other timber-based projects in cities more inclined to support them.

The Northeast is historically fire-conservative. It’s also the cradle of the U.S. steel industry, which, along with concrete, masonry and union concerns are hitting back against CLT proponents angling for market share. The National Ready Mixed Concrete Association last year started the “Build with Strength” public relations campaign to promote steel and concrete and warn against wider use of mass timber products.

One recent email blast about a failed attempt to allow some wood-framing in Florida school construction was headed, “Florida Building Commission Stands Strong for Students.”

Ethan Martin is an engineer serving as technical director of WoodWorks, a campaign of the Wood Products Council to promote mass-timber products. He said the steel and concrete industries lobbied in the 1950s and 1960s to get those products more widely used.

“At this point, they literally have 100-percent market share of anything over five stories. So even if there are only 10 buildings a year built using CLT, that’s going to cut into their market share,” Martin said.

Andrew Waugh, a prominent British CLT proponent, estimates that in Europe, where CLT has been in use since the 1990s, the product represents about 0.5 percent of building materials used in buildings taller than five stories.

Getting the code changed to allow CLT is important, but Greg Kingsley, head of KL&A Structural Engineers and Builders in Denver says that more critical to CLT’s success right now are the local building officials.

Portland officials have made allowances for the use of alternative materials in high-rises. KL&A’s Platte 15 CLT concept was originally planned to be 15 stories, but Kingsley said it was bumped down to five to satisfy the Denver Building Department, which wasn’t willing to make an exception.

“Maybe in the Pacific Northwest, the forest industry is closer to your hearts; in Denver – maybe not so much,” he said. “Look, don’t blame the building officials. They’re just doing their job. They’re waiting for the proof … You should be proud your local building officials in Portland are innovative enough to want to be on the bleeding edge of this.”

CLT isn’t cheap, but can be made due to the speed of construction. Developer Farid Bolouri is hoping to achieve feasibility this way in St. Johns, where residents often are hostile toward intrusive developments. Alan Jones is designing a dense four-story apartment building on a small, centrally located lot. Cutting down on construction impacts is key to project success, Jones said.

“I’ve been watching (Carbon12) go up. I said, I think we can go faster,” he said.

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