Life cycle carbon impacts of thermal mass and ground coupling in residential buildings

Decarbonising housing requires life-cycle assessments that reflect shifting climate and power-sector trajectories. This study evaluates two full-scale, equal-use dwellings with contrasting thermal configurations: a medium-weight masonry structure directly coupled to the ground (B1) and a lightweight timber-frame on a fully insulated slab-on-ground (B2). A cradle-to-grave, 75-year assessment (2026–2100) integrates three SSP pathways, embodied emissions (A1–A3), operational heating and cooling (B6), and end-of-life (C1–C4). Empirical multi-season monitoring anchors operational baselines; electricity carbon intensity declines stepwise from 400 to 200 to 100 g CO 2 ·kWh −1 across three 25-year periods. Results show that B2's initial heating advantage diminishes as cooling demand rises under warming. By 2100, B1 exhibits consistently lower cradle-to-grave emissions, averaging 7.07 kg CO 2 ·m −2 ·yr −1 compared with 8.15 kg CO 2 ·m −2 ·yr −1 for B2, an ≈8 % reduction. While grid decarbonisation reduces operational burdens for both, thermal mass and ground coupling provide additional resilience, preventing overheating without mechanical cooling in the experimental test bed. • Prospective 75-year LCA anchored in full-scale monitoring. •Thermal mass + ground coupling cut life-cycle CO 2 by ∼8 % vs. lightweight. •Heating gains of insulated slab are erased by rising cooling demand. •No-AC overheating eliminated in B1; B2 requires AC under warming. •Under S1–LOW neutrality, break-even ∼15–16 years; ranking unchanged.