A novel approach to establishing bottom-up LCA-based limit values for new construction

The global construction industry, a significant contributor responsible for 37% of greenhouse gas emissions (GHGe), necessitates immediate and relevant policies to reduce emissions. Consequently, several countries are implementing GHGe limit values in building regulations to initiate mitigation measures. To support this development and the efforts to mitigate GHGe, this study provides a method for defining a representative case sample of conventional practice and bottom-up Life Cycle Assessment (LCA)-based limit values for policy measures. Based on a dataset of 291 actual building projects, a representative case sample of 163 conventional case studies is defined, and their related life cycle GHGe is calculated with LCA, resulting in a variation from 8.3 to 11.8 kg CO2e/m2/year. Cumulative distribution functions are computed with share factors, which consider the construction activity in a country and reflect the physical output of completed construction work from which limit values are derived. A general limit value is calculated at 9.0 kg CO2e/m2/year, corresponding to the median where the ambition level targets 50% of new construction to perform mitigation efforts. Across building types, limit values vary between 8.2 and 11.5 kg CO2e/m2/year, and more ambitious limit values for residential buildings are derived starting at 4.9 kg CO2e/m2/year based on examples of best practice case studies. Comparing the general bottom-up limit value against top-down targets reveals a gap, suggesting a necessary increase in the ambition level. Yet, limit values should be introduced and gradually tightened to reach net zero in 2050 across several building typologies to support the adaptation of mitigation strategies.