Cradle-to-Grave Environmental Impacts of Mass Timber Construction in the United States: A Comparative Assessment to Conventional Construction Materials

Abstract

The use and end-of-life (EOL) phases of mass timber products (MTP)—including cross-laminated and glue-laminated timber—remain comparatively understudied in life cycle assessment (LCA) literature, leaving uncertainty around their cradle to grave environmental performance relative to conventional construction materials. This dissertation addresses that gap by building on assumptions used in prior U.S.-based LCA studies of MTP and other structural materials.A comprehensive environmental assessment was conducted for two case study buildings: Google’s “MT1” mass timber building and an alternative reinforced concrete design. Material-specific impacts were evaluated across all life cycle phases—production, construction, use, and EOL—along with carbon storage benefits and product substitution benefits associated with reuse, recycling, and energy recovery. Primary and secondary data were used to quantify material and energy inputs, and multiple EOL scenarios were modeled, including reuse, recycling, incineration, and landfill. Cradle-to-grave impacts were then compared under two waste management pathways: a Business as Usual (BAU) demolition scenario with minimal wood recovery, and an Optimistic deconstruction scenario with recovery of MTP for reuse. Mass timber construction showed consistently lower global warming, acidification, eutrophication, smog formation, and ozone depletion impacts (-10% to -50%) than concrete in the production, construction, and use phases, but higher impacts during EOL treatment when MTP was not recovered (11% to 900%). Reuse of MTP in the Optimistic scenario reduced impacts in most categories; although diesel use during waste processing increased acidification and smog formation, these increases were more than offset by substitution benefits, yielding net reductions across all impact categories relative to landfilling. Accounting for temporary biogenic carbon storage using a dynamic radiative forcing framework—rather than applying conventional ISO carbon accounting rules, which credits higher storage to landfilling—further highlighted the climate benefits of reused MTP. Under the BAU scenario, MT1 outperformed the concrete building (-8% to -61%) on a cradle-to-grave scope in all categories except eutrophication; when MTP was reused, eutrophication impacts became comparable between the two designs. Overall, the findings demonstrate that mass timber construction offers clear cradle-to-grave environmental advantages over reinforced concrete, particularly when structural MTP is recovered for reuse. While landfill disposal can obscure these benefits under ISO carbon accounting, circular economy pathways—reuse, reprocessing, recycling, and energy recovery—consistently reduce environmental burdens and improve climate outcomes. The results underscore the decisive influence of carbon accounting methods and the need for frameworks that recognize the climate value of temporary biogenic carbon storage.