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Background and aim: The construction industry contributes approximately 19% of global greenhouse gas (GHG) emissions and accounts for one-third of worldwide energy consumption, underscoring its pivotal role in addressing climate change. This study evaluates the environmental impact of preserving an existing concrete structure versus constructing a new one with cross-laminated timber (CLT) or virgin concrete.

Methods and data: The effectiveness of environmental comparison in mitigating carbon emissions and reducing resource consumption is investigated through a comparative lifecycle analysis of reuse and replacement scenarios. Utilizing the Life Cycle Assessment (LCA) framework, three scenarios were analysed: (1) preserving existing concrete floors on-site and adding two cross-laminated timber (CLT) extensions, (2) demolishing the existing concrete structure to construct an entirely new five story building using CLT, and (3) demolishing and constructing a new five story structure with cast-inplace virgin concrete. The analysis comprehensively quantifies the Global Warming Potential (GWP) across the production, operational, and end-of-life stages.

Findings: Results demonstrate that reusing existing concrete floors reduces approximately 40 kg CO₂e/m² gross floor area compared to a new timber construction and 121 kg CO₂e/m² tons compared to new concrete construction.

Theoretical/practical/societal implications: The results highlight the environmental benefits of implementing circular economy principles into construction practices.