Exploring embodied greenhouse gas (GHG) emissions of mass timber construction: A comparative study of life cycle assessment databases

With global efforts in reducing building operational energy consumption, attention is increasingly turning toward mitigating embodied greenhouse gas (GHG) emissions from building materials manufacturing and processing, particularly for emerging materials like mass timber. Quantifying embodied emissions typically requires the use of GHG emission coefficients from life cycle assessment (LCA) databases. However, significant variability persists in the results of LCA studies while their underlying causes remain largely unexplored. Therefore, this research aims to compare embodied GHG emissions data of mass timber across five widely used LCA databases (Ecoinvent, AusLCI, EPiC, ICE, and ÖKOBAUDAT). Through detailed examination at material and building levels, the research reveals significant methodological inconsistencies that create substantial variations in embodied emissions. At the material level, mass timber emissions span from -686.80 to 1718.00 kgCO₂eq/m³. Building-level analysis (A1-A3) reveals emission ranges of -170.31 to 434.62 kgCO₂eq/m² for mass timber construction and 69.79 to 485.95 kgCO₂eq/m² for concrete buildings. The study identifies several challenges in current mass timber LCAs, including inconsistent treatment of biogenic carbon flow, varying system boundary definitions, and inadequate consideration of End-of-Life (EoL) processes for mass timber. Regional variations in manufacturing processes, energy sources, and transportation distances emerge as essential factors influencing data quality. This highlights the need for establishing standardized approaches for biogenic carbon accounting, implementing detailed material documentation systems, and developing more comprehensive and transparent databases to enhance the reliability of mass timber LCA.