Scrutinising embodied carbon in buildings: The next performance gap made manifest

Life cycle assessment (LCA) is becoming increasingly mainstream as an early-stage design-decision tool for buildings. Still, there are considerable variations in how the method is currently used, leading to limitations in comparing the results and the conclusions that can be drawn. These variations are due to several factors and LCA modellers must make multiple methodological decisions during an assessment. This has resulted, unsurprisingly, in a variety of approaches, and a wide range of outcomes. Academics have produced numerous case studies on particular buildings, aiming towards a detailed understanding of the energy and carbon impacts. However, very few case studies are detailed enough to allow for an in-depth comparison. This article investigates in detail these embodied carbon assessments, considering the data used and the methodological assumptions made. An in-depth analysis shows that there are still considerable variations in how the methodology is applied, leading to substantial limitations in comparing results and drawing conclusions. Results may differ by two orders of magnitude, thus limiting the understanding of how real mitigation might best be achieved. Without immediate action, embodied carbon will become a 'second wave' of performance gap in environmental assessments of buildings. Both greater transparency and greater conformity must be embraced by the LCA community and enforced by policymakers and professional bodies.