Biogenic Wall Systems for NZEB Single-Family Houses: Life-Cycle Carbon, Primary Energy Use and Architectural Implications

This study examines the environmental implications of envelope material choices for Nearly-Zero-Energy Building (NZEB) single-family houses in carbon-intensive energy contexts. Using a comparative Life Cycle Assessment (LCA) based on EN 15804+A2, a 100 m2 house was analysed over a 50-year lifespan across three archetypes: ceramic masonry (Design 1), solid log (Design 2), and timber–straw (Design 3). By maintaining a common steady-state thermal standard (U ≤ 0.20 W/(m2·K)) across all variants, the study provides a controlled comparison in which differences in GWP and non-renewable primary energy use primarily reflect material choices rather than insulation level. While both biogenic designs achieved negative embodied Global Warming Potential (GWP) in modules A1–A3 due to carbon sequestration, the results also show that structural concept and detailing strongly influence resource efficiency. Design 3 required substantially less timber volume than Design 2 while maintaining a comparable thermal standard and the lowest PENRT_A1–A3. Under the fixed operational assumptions adopted in this comparative study, module B6 remained the dominant single life-cycle contributor in all variants. The timber–straw system is therefore interpreted here as the more resource-efficient envelope strategy, whereas the solid-log solution primarily maximises timber-based carbon storage.