Comparative Assessment of the Carbon Footprint of on-site and off-site Wall Element Constructions

Off-site construction is considered as environmentally preferable to on-site due to the controlled environment for planning and production before assembly in the construction site. However, evaluating the actual environmental benefits and drawbacks from a life cycle perspective is important to avoid problem shifting. The aim of the paper is to evaluate the environmental performance of conventional on-site construction of wall elements, in comparison with off-site wall element production in a factory and assembly on the construction site. This study has been a collaboration with a Norwegian contractor using wall constructions with elements produced either on- or off-site. The contractor seeks to reduce the negative environmental consequences from building activities by establishing a local factory for off-site element production, thus motivating this study to provide environmental inputs to a decision-making process. The wall elements which either fulfil the Norwegian building code (TEK17) or passive house (PH) standard are evaluated using three scenarios: 1) on-site construction with local materials obtained from Norwegian manufacturers/suppliers, 2) off-site wall element production and wall construction in Norway, and 3) off-site wall element production in Estonia and wall construction in Norway. The GHG emissions from the scenarios are calculated using screening LCA method for life cycle stages of production (A1-A3) and construction (A4-A5). The results show that lowest GHG emissions are attributed to local Norwegian off-site TEK-wall element production, whereas the Norwegian on-site PH-wall has the highest GHG emissions. The results also highlighted the contribution to GHG emissions of specific building materials, as well as the dependency of the results on the background data and the methodological choices used in the study.