Input–output and process LCAs in the building sector: are the results compatible with each other?

Buildings are a major contributor to climate change. Use phase has traditionally been the focus area, but the importance of construction-phase has increased with the emergence of energy-efficient buildings. Life-cycle assessment (LCA) is arguably the best method to assess and analyze the emissions caused by buildings. However, within LCA there are two very different approaches – process LCA and input–output (IO) LCA – which lead to different results. When looking at the scale of published LCA results, it is evident that IO LCAs are placed at the top end, and process LCAs at the bottom end. It is thus questionable whether LCA can provide data that can be used for decision-making and policy formation. This study takes a step toward filling this gap by presenting a comparison of process and IO LCA results of the pre-use phase of a residential concrete element building in Finland. Exactly the same scope is utilized in order to maximize comparability. The results depict how the two main LCA methods produce significantly different results. The implications of acknowledging this are discussed. The results fall in midway between the extremes published using the two methods but still deviate from each other by a multiplier of almost 2.