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How Green Are Mass Timber Buildings?

Advocates say that mass timber could revolutionize the building industry, but some skeptics worry about the environmental impact of logging

A seven-story mass timber building in Minneapolis called T3 opened in 2016. At the time, it was the largest heavy timber building in the U.S. [Image credit: Ema Peter]

This post originally appeared at Yale Environment 360.

The eight-story Carbon 12 building in Portland, Oregon, is the tallest commercial structure in the United States to be built from something called mass timber.

If the many fervent boosters of this new construction material are right, however, it is only one of the first mass timber buildings among many, the beginning of a construction revolution. “The design community in Portland is enthralled with the material,” said Emily Dawson, an architect at Kaiser + Path, the locally-based firm that designed Carbon 12.

The move to mass timber is even farther along in Europe. That’s because mass timber — large structural panels, posts, and beams glued under pressure or nailed together in layers, with the wood’s grain stacked perpendicular for extra strength — is not only prized as an innovative building material, superior to concrete and steel in many ways, it is also hoped it will come into its own as a significant part of a climate change solution.

Among architects, manufacturers, and environmentalists, many want nothing less than to turn the coming decades of global commercial construction from a giant source of carbon emissions into a giant carbon sink by replacing concrete and steel construction with mass timber. That, they say, would avoid the CO2 generated in the production of those building materials and sequester massive amounts of carbon by tying up the wood in buildings for decades or even longer, perhaps in perpetuity.

“Say the typical steel and concrete building has an emissions profile of 2,000 metric tons of CO2,” said Andrew Ruff, of Connecticut-based Gray Organschi Architecture, a leading proponent of the laminated wood revolution. “With mass timber you can easily invert so you are sequestering 2,000 tons of CO2. Instead of adding to climate change you are mitigating climate change. That’s the goal.”

And it is taking off. Mass timber has a two-decade track record in Europe. The 18-story Mjösa Tower just opened last month in Norway. An 18-story mass timber building was recently built in Vancouver as well, and an 80-story high-rise is proposed for Chicago. There are new commercial mass timber buildings in London, Atlanta, and Minneapolis. Some 21 timber buildings over 50 meters (164 feet) tall will be completed in Europe by the end of the year, according to one report.

Critics challenge environmental benefits

But there are big questions being asked about just how sustainable the new building material is — especially about how forests that produce mass timber are managed, and how much CO2 would be emitted in the logging, manufacture, and transport of the wood products used in the construction. So far, critics say, there aren’t good answers to these questions.

Carbon 12 in Portland, Oregon is the tallest building in the United States made with mass timber.
Carbon 12 in Portland, Oregon, is the tallest building in the U.S. made with mass timber.  [Image Credit: Kaiser + Path]

“We want to debunk the myth that mass timber is in any way, shape, or form related to some kind of environmental benefit,” said John Talberth, president of the Center for Sustainable Economy, which is based near Portland. “That’s simply not true.”

Yet proponents say that mass timber does have real promise as a way to sequester massive amounts of CO2, if a fully sustainable life cycle comes together. “We are working with a large interdisciplinary team of climate scientists, carbon cycle researchers, metallurgists, and foresters to really understand the potential climate impacts of mass timber at scale,” said Ruff.

A lack of understanding of the full CO2 picture has not kept the field from taking off. The burgeoning demand for mass timber posts and beams has seen sawmills open in the timber towns of the the U.S. Northwest and loggers go back to work to harvest the pine, fir, and spruce used in the manufacture. The first certified U.S. producer of mass timber opened in Riddle, Oregon, in 2015. Other producers have either recently opened or soon will. Analysts call it a revolution in building and the next great disruption of the construction industry, for a number reasons that have nothing to do with the environmental aspects.

“Because its components are fabricated off-site to [precise specifications], it goes together really fast on site,” said Dawson. “So you can cut months off the construction time. It’s more predictable than concrete. You can work through cold weather and don’t have to worry about the temperature tolerances of concrete. It’s also a lot quieter than other kinds of construction, so you can be a good neighbor.” It’s stronger than steel, lighter, and, surprisingly, may be as fireproof.

Architects say the exposed wood interiors in these buildings are warmer than other materials and far more aesthetically pleasing. Michael Green, who builds mass timber structures in British Columbia, said some people walk into buildings he has designed and want to hug the wooden interiors. The dense laminated beams also hold up well to fire, unlike other kinds of wood construction.

Mass timber can be cheaper than concrete and steel, depending on where it is sourced. And when production is scaled up across the globe, experts say, mass timber should be considerably cheaper.

Unanswered questions about mass timber’s life cycle

The possible prodigious climate benefits, though, are what has many people taking mass timber seriously. These benefits come because of two big facts about commercial construction. First, CO2 emissions from the building industry account for about 40% or more of global CO2 emissions. And the manufacture of concrete and steel each contribute about 5% of global emissions.

Using mass timber for commercial construction could greatly change that equation. But there are key questions about the life cycle of mass timber, and some say the industry doesn’t have enough data yet to back up its claim that it is a major climate change solution.

After the building has run its course, the beams would need to be stored without decomposing or re-used without releasing the CO2 in order to make the carbon equation work. And there are numerous unknowns about how much CO2 would be expelled in the logging, manufacturing, and transport of mass timber products. The forest products industry is already the largest source of CO2 emissions in Oregon because of fuel burned by logging equipment and hauling trucks, the burning of wood, and the decomposition of trees after they are cut.

Beverly Law, a professor of global change biology and terrestrial systems science at Oregon State University who headed up the Oregon forest study, says there hasn’t been a thorough analysis of carbon emitted by mass timber production because it is enormously complex to track the factors that produce CO2 in forest ecosystems and in production. Some of the data needed, she said, is incomplete or absent. It took her team of researchers more than a decade of analysis to figure out that the Oregon wood products industry was the largest emitter of CO2 in the state, Law said.

“We looked at long- and short-term products, what mills burn for heat, fuel burned for harvesting, transporting from forest to mills to end use, and emissions along the way,” she said. Another major issue is how long the wood will be in use, which is not yet known. In addition, Law said, any analysis of CO2 must account for how much the forest is taking up before and after logging, “and a lot of people don’t pay attention to that part of it. We just don’t have the information to run this through a life cycle assessment.”

Sustainable forestry claims are challenged

The forestry part is what has some skeptical of how ecologically sound mass timber is and, if and when it’s scaled up, whether it will truly provide a planetary climate solution. In a letter to the city of Portland last year, representatives of Oregon environmental groups — including the Audubon Society, the Sierra Club, and Oregon Physicians for Social Responsibility — raised serious doubts about mass timber as a green climate solution and questioned the city’s plan to use it.

First and foremost, they said, is the need to certify that wood is logged sustainably and certified as such. “Without such a requirement,” the letter stated, the city “may be encouraging the already rampant clear-cutting of Oregon’s forests… In fact, because it can utilize smaller material than traditional timber construction, it may provide a perverse incentive to shorten logging rotations and more aggressively clear-cut.”

Such industrial-type forestry — large-scale plantings of trees selected to grow fast — creates a “biological desert,” said Talberth, of the Center for Sustainable Economy. “And it’s driving the extinction of thousands of species. Mass timber is mass extinction.”

“We must ensure that mass timber drives sustainable forestry management, otherwise all of these benefits are lost,” agreed Mark Wishnie, director of forestry and wood products at The Nature Conservancy. “To really understand the potential impact of the increased use of mass timber on climate we need to conduct a much more detailed set of analyses.”

Wishnie said The Nature Conservancy, the U.S. Forest Service, and a dozen universities and other research institutions are launching a new analysis of mass timber.

At the same time, he said. “there is enough data to say the [CO2] savings are significant.” He said the substitution of concrete and steel with wood and the long-term carbon storage in mass timber buildings make up about 75% of the total benefit, and the forestry end, if executed sustainably, about 25%.

While there is disagreement on many points, making the mass timber movement work, proponents say, is essential. “If you look 30 years down the road to 2050, we’re projected to have 2.3 billion new urban dwellers,” said Ruff. “That is a huge amount of construction. Every day that goes by that we don’t convert from mineral-based extractive construction techniques to carbon sequestering building systems, we tend to dig ourselves further in a hole.

“So,” he added, “the question is, how can we grow this fast enough to be a solution for climate change?”

 

Jim Robbins is a journalist based in Helena, Montana.

13 Comments

  1. John Prospect | | #1

    It is good that they are studying this more closely, but some of the comments in the article seem a bit one-sided. I grew up in a logging town and know first hand that forest management is not always done well. However, we are really in a situation of: concrete vs wood - which do you prefer? Do we really think concrete is the more green solution?

    I am not an expert, but I would not make that wager.

    The real solution is to build smaller, smarter, and to last. This goes for any material. There are plenty of very old wooden buildings in the world and we can make modern ones last well if we want to.

    (And the zero-overhang Carbon 12 building made me cringe. I sure hope they have a bomb-proof 100-year rainscreen.)

    Edit: And hopefully the renewed interest in wood will bring increased interest in good forest management, so we don't end up with monoculture plantations.

  2. Peter L | | #2

    It always comes down to profits and money. The timber industry sees huge $$ profits in building high-rise wood buildings. So they will fight for that market share and if that takes creating and paying for "rigged & bias" studies, follow the money trail.

    My bet is on the concrete buildings when it comes to longevity and strength.

    Soon the timber industry will be trying to build bridges and highway overpasses out of mass timber.

    1. Malcolm Taylor | | #3

      The weakness of both concrete and wood structures is exposure to the elements. If the integrity of the building envelope is maintained there is no reason to believe either will fail. However the longevity of buildings, tall or otherwise is almost never determined by their structural life. It is a function of their usefulness over time, demographic and economic shifts, style and fashion. If a building maintains its usefulness it will have along life. If it doesn't, the robustness of its structure won't save it.

  3. user-7230765 | | #4

    I'd encourage anyone with an interest in the carbon impacts of mass timber to check out this article on Treesource.org which analyzes the research and assertions made by Beverley Law regarding the carbon impact of wood. https://treesource.org/news/climate/analysis-in-zeal-to-restrict-logging-advocacy-groups-exploit-dubious-research/ In brief, the researchers base their calculations on a number of dubious assumptions that substantially change the outcomes; among them is the use of a 30-year lifespan for buildings as opposed to the internationally accepted ISO protocol of 75 years. If we are only building 30-year structures we have bigger problems than the ability to calculate carbon sequestration.

    1. Deleted | | #6

      “[Deleted]”

    2. Malcolm Taylor | | #7

      User... 765,

      Thanks for the link.

      My modest contribution to timber infrastructure:

      1. User avater GBA Editor
        Martin Holladay | | #8

        Malcolm,
        Fun place to work! Did anybody drop a tape measure or framing square into the water?

        1. Malcolm Taylor | | #9

          Martin,

          I did more frequently than I'd like to admit. At high tide there is about six feet of water in the gap so often when I did manage to get down to retrieve them they were gone.

          The bridge I'm standing on to take the picture is built on a sixty foot cedar log. After 70 years it is getting a bit soft so we decided to retire it.

          Low tide:

          1. John Prospect | | #10

            Great pictures!

    3. John Prospect | | #11

      Thanks for the link to the treesource article, User-7230765. It was remarkably detailed and balanced, I thought. A good supplement to the article posted here.

  4. Markiz_von_Schnitzel | | #12

    Is there a study that has conclusive answers to how long do buildings built by concrete and wood last? And for how long are they occupied? That sounds like a pretty big factor.

    My experience in germany/austria/croatia (central europe) is that there is a LOT more old concrete/clay masonry houses still standing and in use for several generations as opposed to old wooden ones. But of course, this is a subjective feeling, not in any way a fact.

    Likewise, I don't understand the wood vs concrete in the 1st place, at least in residential housing..
    When you bild with wood, you still need concrete foundations, which make >50% of all concrete used in a typical house here. All of the walls are clay blocks (with thin concrete binders, but lately often a type of foam glue), and roof is wooden obviously, also covered in clay.
    So, pretty much, if I did a construction in timber, I would only save the thin concrete between the blocks. Which is much smaller than what I used in foundations.

    1. Malcolm Taylor | | #13

      Markiz,

      People generally build out of what is around them. It isn't surprising that Scandinavia, Russia and much of North America use wood, while the more densely populated regions in Europe, or more arid Mediterranean countries use wood sparingly, and instead opt for masonry.

      The fate of buildings, especially in North America, isn't particularly linked to their structural longevity. Communities wax and wane due to their economic viability, demographics, political change, and to some extent fashion. Individual structures last as long as they are maintained - and people maintain houses they like to live in, in places it makes sense to be. It is tempting to build something more permanent - something that will endure - but the odds are against us.

      Protected from its surroundings by the cladding, the structure, whether steel, concrete or wood should last centuries. Once the cladding is left to decay all buildings decline quickly. Europe is filled with abandoned villages and houses. They may look more picturesque that their North American counterparts, but they are just as uninhabitable and difficult to remediate.

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