Comparative life-cycle assessment of mass timber housing: A sustainable pathway toward Chile's climate mitigation goals

Looking ahead to ambitious climate-mitigation goals, developing countries are now facing the dilemma of having to deal against soaring housing demands and drastically reducing the environmental impacts of housing. In Chile, existing housing stock is projected to double by 2050, intensifying energy consumption, carbon dioxide and equivalent greenhouse gas emissions. As an alternative to mainstream concrete, the emergence of mass timber (MT), primarily in the form of cross-laminated timber (CLT) and glued-laminated timber (glulam), offer a pivotal opportunity to reduce carbon-equivalent emissions and temporarily store significant amounts of biogenic carbon. This study investigates the environmental impacts of mid-rise MT housing with integrated passive-envelope designs and compares it with mainstream reinforced concrete (RC) equivalents. Results indicate that, under current housing regulations, substituting traditional RC framing with MT systems of CLT and glulam may inadvertently increase Global Warming (GW) impacts, along with up to 17 additional environmental impact categories evaluated in this study. Extensive life-cycle analyses of twelve five- and eight-story case studies showed that while substituting RC with MT could lower the GW of mainstream mid-rise housing by 0.13–29% in three pair of cases, it increased by 4–13% in the other three. However, the biogenic carbon stored in MT members, accounting for 378–446 kg CO₂-bio/m², was sufficient to offset the GW of product and construction stages and achieve net life-cycle savings of 24–72%. Moving forward, passive envelope designs performed to MT buildings demonstrated that the GW of space-conditioning over the use stage (465–1100 kg CO₂-eq/m²/50-yrs) could be reduced by 76–84%, increasing scope for achieving a negative GW balance. Finally, the paper explores policy and design recommendations for scaling MT housing to achieve carbon-equivalent neutrality goals by 2050.