The biggest new idea in sustainable building is also one of the oldest construction materials around: timber. But this isn’t ordinary wood. Cross-laminated timber, as it’s known, is arguably the first major structural innovation since the invention of reinforced concrete more than 150 years ago.
Cross-laminated timber itself has been in use for decades, particularly in Austria and Germany. Interest in the material is surging along with concern about the greenhouse-gas emissions associated with concrete and steel. The production of construction materials such as steel, cement and glass accounts for 10% of global energy-related CO2 emissions, according to a United Nations report.
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| The operation and construction of buildings accounted for more than a third of global energy-related CO2 emissions in 2020. Image: UNEP 2021 Global Status Report for Buildings and Construction |
Green-building benefits
By contrast, cross-laminated timber and other engineered wood products can benefit the climate in three ways: trees capture and store carbon as they grow; long-lived wood products lock in carbon; and these products can be used instead of high-impact materials like concrete in many cases.
Crucially, these products - often referred to under the catch-all term “mass timber” - are strong enough to replace concrete and steel in many of the taller buildings going up in cities around the world. And they have inherent fire-resistant properties that allow their use on a commercial scale, according to Lisa Podesto, Senior Business Development Manager at Lendlease, a global real-estate and investment company that has built more than 20 cross-laminated timber structures.
Competing with concrete
“The beauty of this new product type - mass timber - is that it’s competing in a market space with materials that timber couldn’t compete with in prior building generations,” Podesto said during a panel discussion at the World Economic Forum’s Sustainable Development Impact Summit 2021. “It’s opening opportunities to offset carbon in a different landscape.”
The carbon-reducing impact of green building with mass timber goes beyond the sustainable forests that produce these products and the carbon they lock away. While concrete is essential in foundations, timber buildings are lighter so those foundations can be smaller. Mass-timber products are modular and can be produced in a factory, which means faster construction, fewer trucks delivering materials and less disruption to communities around building sites.
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| At 85.4 metres, the Mjøstårnet building in Norway is the tallest timber-frame structure in the world. Image: Voll Arkitekter |
Mass timber set for take-off
“Mass timber is likely to take off at scale over the next decade,” said Caitlin Clarke, Senior Conservation Fellow, Supply Chains at The Nature Conservancy, during the panel discussion.
Yet, while the use of mass-timber products can contribute to climate solutions in some places, there’s no one-size-fits-all approach that can be applied around the world, according to Clarke. We need to know more about how increased use of mass timber would affect forests, the carbon they store and the ways we manage them. The Nature Conservancy is part of a broad research effort to model the impact of mass-timber demand on forests.
“We’re doing scientific research that is informing how this is going to happen, and working on safeguards to help inform how it should happen,” Clarke said.
Long-term investment
Making cross-laminated timber panels is straightforward. Layers of lumber cut from a single log are glued together, with each layer sitting perpendicular to those around it. The panel is then hydraulically pressed to achieve strength.
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| Cross-laminated timber panels consist of no fewer than three cross-bonded layers of timber, typically ranging in thickness between 20mm and 45mm. Image: Structural Timber Association |
The production of mass timber drives demand for larger pieces of wood - and larger trees. And that means different sustainable forest-management techniques designed to yield products that will be in use, and storing carbon, for a long time.
The challenge for firms that own and manage forests, and manufacture mass timber is that bigger trees take longer to grow, meaning they could be waiting 40, 60, even 80 years after planting to get a return on their investment, according to Ara Erickson, Vice President for Corporate Sustainability at Weyerhaeuser. The sustainable-forest products company has about 11 million acres of timberland in the US and manages millions more under long-term licences in Canada.
Hit the go button
One benefit of mass timber is that we’re driving increased demand for larger pieces of wood, and larger trees, as well as solid products that stay in use for longer, Erickson said on the Forum panel.
And that demand is critical for firms like Weyerhaeuser to carry on replanting and managing their forests, rather than giving land over to agriculture or other uses. So, the industry needs to continue making the case for the benefits of mass timber to drive take up, she said.
“We have science and data to show that,” Erickson said. “It’s deciding that we’re ready to go do it. That’s our challenge - do we hit the go button?”
Mass timber has been around for decades, and a lot of the work to prove its usefulness has been done. Many of the technical barriers have been cleared and fire-safety issues have been worked out, according to Vincent Martinez, President of Architecture 2030, a non-profit think tank created to help reduce the climate impact of the built environment. Building codes are also opening up opportunities for taller mass-timber structures in many places.
“The biggest challenge now is changing social perceptions of mass timber, so the industry has a green light to step up development,” Martinez said on the panel.
That means using global events such as the Sustainable Development Impact Summit to start debunking misperceptions, such as that increased use of mass timber would lead to deforestation.
“What we’re trying to do is break down these myths in these dialogues to say - we can get started, and we can keep making improvements in this process,” he said. “Turn that light green.”
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