Life Cycle Assessment of a Swedish Multifamily Building Designed for Disassembly and Flexibility: Impact of Allocation Methods on Future Scenarios

Quantifying the environmental benefits of designing buildings for disassembly and flexibility (DfD/DfF) remains challenging within current life cycle assessment (LCA) frameworks. This study assesses the climate impact of a two-story Swedish timber multifamily building (377 m2) designed for future transformation and reuse. An LCA covering modules A–D was performed for one linear scenario (S0: demolition without reuse) and three circular scenarios (S1: layout change, S2: relocation, S3: vertical extension), applying three allocation methods: 100:0, 50:50, and system expansion. All circular scenarios reduced climate impact compared to the linear reference, though to varying degrees. Reductions ranged from 8–50% within the system boundary (A–C), depending on scenario and allocation method. While the 50:50 approach attributed significant reductions within A–C, the 100:0 method emphasized benefits primarily in module D. The 50:50 method yielded the lowest impacts within the system boundary, whereas system expansion showed the largest overall reductions but relied on uncertain assumptions. The study concludes that including future scenarios in LCA is more effective in promoting circularity than the specific choice of allocation method. It emphasizes the need for standardized frameworks that account for multiple use cycles and support fair comparisons in policy and procurement.