Reversible Bio-Based Prefabrication as a Carbon Sink: Whole-Life Cycle Assessment of a Straw Passive House in Germany

This study evaluates the embodied and operational energy and carbon performance of a prefabricated straw-based single-family Passive House in Germany, demonstrating the potential of biobased construction for building-sector decarbonization. A standardized life-cycle assessment (LCA) was conducted in accordance with EN 15978, covering embodied impacts in stages A1–A3 using Ubakus and operational energy in stage B6 using DesignBuilder over a 50-year service life. Global warming potential (GWP) and non-renewable primary energy demand (PENRT) were assessed at material, component, and whole-building levels. The building incorporates a highly insulated envelope (U < 0.15 W/m²K), where straw enhances thermal insulation, reduces embodied carbon, and improves passive performance. Results show that straw insulation exhibits negative embodied carbon at the material level (−40 kg CO₂e/m²) due to biogenic carbon sequestration. At the component scale, prefabricated straw infill timber wall systems act as carbon sinks (−38 kg CO₂e/m²) while maintaining moderate embodied energy demand. At the building scale, the total embodied carbon remains negative, confirming the dominant contribution of biobased materials. Operational performance is also significant, with a heating demand of 12.95 kWh/m²·year and total primary energy use of 45.10 kWh/m²·year, meeting Passive House requirements. However, windows remain a major environmental hotspot, contributing disproportionately to embodied carbon and energy impacts. Overall, the findings demonstrate that combining straw-based prefabrication with passive design strategies can substantially reduce both embodied and operational impacts, supporting the transition toward low-carbon and energy-efficient buildings within European regulatory frameworks.