Mass timber construction is widely considered an excellent option for reducing buildings' total life-cycle carbon emissions because wood is a carbon sink. Mass timber materials such as cross-laminated timber (CLT) panels, manufactured by gluing layers of timber boards with grains at right angles, can be used for all of the major load-bearing elements of a building, and thus offer an alternative to carbon-intensive concrete and steel construction with the potential for substantially lower life-cycle carbon emissions. Current options for sourcing mass timber materials in North America are limited compared to traditional construction materials; as a result, mass timber vendors that can meet project cost and schedule requirements might be quite distant from the construction site. However, most environmental impact assessment studies have not considered the implications of transportation impacts within the mass timber panel supply chain when calculating life-cycle impacts. Our model specifically enables investigation of the embodied primary energy and global warming potential (GWP) of supply chain decisions regarding the type of timber species used, the region of the U.S. it is sourced from, and the location of the mill. Results show that longer transport distances in the supply chain for raw timber and mass timber components can contribute as much as 21% of the embodied primary energy of a mass timber building, and the use of a higher-density timber species increases this contribution to 24%, with most of that energy derived from fossil energy sources. For perspective, the GWP of a building whose mass timber components have been transported over 6,000 km is greater than the GWP of a reinforced concrete building. Thus, factors like the location of mass timber production facilities and the type of timber species can significantly impact the overall life-cycle assessment and, if chosen appropriately, can mitigate the environmental impacts of mass timber construction. The model focuses particularly on construction using CLT panels as the load-bearing panel type, though the findings are generalizable to mass timber construction using other joining methods for the panels.

Implications of material sourcing for mass timber construction: Embodied energy and carbon impacts of transportation

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