The Impact of the Bill of Quantity Export Process from BIM on the Accuracy of the LCA Results

The construction industry is responsible for a significant amount of greenhouse gas emissions. Therefore, buildings have the potential to play a central role in climate change mitigation. It is also known that building projects are unique and complex, which is why a high degree of process automation is necessary. Two key methods can be employed to calculate the environmental impacts of a construction process: Building Information Modeling (BIM) and Life Cycle Assessment (LCA). Currently, both methods are being considered as a part of advanced building projects. Database (BIM) models can be used as a precise inventory of materials and as an input for LCA. This study aims to (1) review the current status of published BIM-LCA workflows, (2) use a common case study among participants from various countries to compare the individual workflows and the calculated results, (3) identify potential sources of errors in all workflows on the common case study, and (4) provide recommendations and suggestions for developing BIM-LCA models based on the example of the common case study. The outcomes show that the main sources of differences emerge from not including all materials or from the inconsistencies in the exported material lists of the bill of quantities. The reasons for the missing materials stem primarily from the inadequate decomposition of composite materials, oversight of certain materials, and exclusion of thin materials such as foils. Inconsistencies arise from the incorrect handling of composite materials, the grouping of similar materials, and rounding inaccuracies. These issues highlight that errors occur early in the life cycle inventory phase, which forms the foundation of subsequent LCA phases, thereby impacting the final results and potentially leading to inaccurate assessments of environmental impacts. Ensuring accuracy at this stage is therefore critical for supporting reliable sustainability assessments. Consequently, recommendations are proposed to mitigate errors across various stages of the process to enhance the accuracy of LCA outcomes.