Influence of inventory cutoff rules on whole-building LCA results

Abstract

The scarce publications on whole-building lifecycle assessment (wbLCA) highlights the need to reduce the number of flows considered. Cutoff rules facilitate inventory modeling, but their effects are underexplored in the literature. This work investigates how the most well-known cutoff approaches used in wbLCA - by mass and energy, as indicated by the EN 15804 standard, and by building elements, as adopted by LEED v4 certification – influence the assessment results, relatively to a baseline, complete inventory. Cradle to grave impacts was calculated for two case studies. SimaPro v8.5/9.0 supported processes composition and adaptation from the Ecoinvent database. CML-IA baseline and CED methods were used for impact assessment, and k-means clustering highlighted relationships amongst environmental categories. Whilst the European cutoff rule retains a considerable share of impacts on all categories, the elements excluded by the LEED approach mostly impact non-assessed categories, such as ecotoxicity, human toxicity, and abiotic depletion. These categories are highly affected by some building materials production. The free choice of three environmental categories to assess may also result in information redundancy whenever they pertain to the same cluster. To balance inventory completion viability while ensuring the integrity of wbLCA conclusions, we recommend that the certification compute over 75% of the metals used in the building and strategically expand the set of categories evaluated on a mandatory basis. Additional studies are now needed to confirm our findings and validate propositions for certification-oriented wbLCA.