Sequestering Carbon in Cross-Laminated Timber

By Chris Schnepf

Panel of five layers of boards glued together perpendicular to each other.

Cross-laminated timber panels are made by gluing together three or more layers of boards perpendicular to each other. Photo: Chris Schnepf.

Most of the articles on AgClimate.net focus on adaptation; that is, how we manage fields, forests, and rangelands to adapt to anticipated changes in climate. But there is another side to dealing with climate change—how do we reduce the amount of carbon dioxide in the atmosphere? These efforts are collectively referred to as “mitigation”.

Most of our mitigation focus has been on practices to reduce emissions from cars, tractors, planes, manufacturing, livestock, etc… anything that puts greenhouse gases into the atmosphere. But another part of the mitigation discussion focuses on techniques to place carbon where it can be stored long term and kept out of the atmosphere. In forestry and agriculture there is a lot of research underway on practices that sequester more carbon, from changing agricultural practices, using biochar as a soil amendment in agriculture, to managing forests in ways that retain more carbon, within fire safety limitations.

One of the unique dimensions of carbon sequestration in forestry is how materials generated in forest management are used. Carbon stored in food and feed has a relatively short path to the atmosphere as we—or livestock—eat it and exhale greenhouse gases. In contrast, forest products are commonly sequestered in wood products (houses, furniture, etc.) for decades or even centuries. Even paper products often last longer than food (how old are your oldest books?) and are frequently recycled for additional longer life. (If you want to learn more about carbon life cycles for forest products, see Lippke and colleagues’ “Life Cycle Impacts Of Forest Management And Wood Utilization On Carbon Mitigation: Knowns And Unknowns.”)

You may have read recently about a class of wood products called “mass timbers”. The American Wood Council defines mass timber as “any product currently permitted for use in Type IV construction, such as cross laminated timber, structural composite lumber, glued-laminated timber, and large section sawn lumber.”

Many of these wood products could also be called wood composite materials. The forest products industry has been gluing and joining pieces of wood to form composite wood products for many decades (e.g., plywood, laminated beams, oriented strand board, etc.) What is different with these new materials is their size and how they are used. As the name suggests, mass timbers are much more massive, and that mass stores a lot of carbon.

Stacked cross-laminated timber panels pre-cut with angles and joints

Cross-laminated timber panels are typically designed for specific building projects. Photo: Chris Schnepf.

One type of mass timber that is getting a lot of attention in the Pacific Northwest is cross-laminated timber or “CLT.” Cross-laminated timber typically comes in the form of a wood panel that is manufactured by gluing together three or more layers of boards (usually more) perpendicular to each other. Cross-laminated timber is used in very different ways than the boards you see in lumber yards. Traditionally, lumber is produced in standardized sizes and is used in a variety of different ways. By contrast, CLT panels are usually engineered for specific building projects. You may have seen articles in the media about buildings from three to 10 stories high or more built with these materials. Some are apprehensive about fire risk with an all-wood building, but experts often say these buildings are actually safer from fire than other types of structures—it takes a fire a long time to burn through a really massive piece of wood.

Mass timbers have been very popular in the media recently, so an internet search will connect you to a lot of articles and photos of CLT in use. For a good research-based primer, go to the “CLT Handbook.” Cross-laminated timber is a relatively new industry in North America, but its use has been growing in Europe for quite some time. The topic is of particular interest in the Pacific Northwest, because several firms here have built plants to produce CLT panels, one of which looks to be the largest producer of CLT panels in North America. That is good news to forest owners who always welcome larger, more competitive markets for their logs. But it is also good news for climate, as buildings made from mass timbers will sequester and store even more carbon than conventionally constructed buildings.  Cross-laminated timber production also has a smaller carbon footprint than metal or concrete building materials.

 

References

FPInnovations. 2013. “CLT Handbook.” US Edition, FPInnovations and Binational Softwood Lumber Council, Point-Claire, Quebec. Available online at https://info.thinkwood.com/clt-handbook

Lippke, B., Oneil, E., Harrison, R., Skog, K., Gustavsson, L. and Sathre, R., 2011. Life cycle impacts of forest management and wood utilization on carbon mitigation: knowns and unknowns. Carbon Management, 2(3), pp.303-333.

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