As operational emissions decline, embodied carbon becomes increasingly important in Europe’s post-war residential stock, where energy and seismic deficiencies may coexist. This research develops and evaluates a BIM/HBIM-based Decision Support Framework integrating Whole Life Carbon (WLC), Life Cycle Assessment (LCA), energy performance, Life Cycle Costing (LCC), seismic evidence, and Multi-Criteria Decision Making (MCDM). A 50-year period and GIFA = 3,848 m² are adopted. Applied to a Type A1 building in Ljubljana, the framework compares five scenarios from existing condition to replacement. MCDM integrates EUI, non-operational GWP, discounted LCC, and EC8-relative seismic resistance derived from external technical evidence; no dynamic seismic analysis was performed as part of this thesis. S1 achieves the lowest WLC (1,108.7 kgCO₂e/m² GIFA) but retains the S0 seismic reference of 9.6%. S3 improves energy, WLC, and LCC relative to S2 while maintaining approximately 98% EC8 resistance. S4 achieves the lowest EUI (163.25 kWh/m²·year), discounted LCC (472.83 €/m² GIFA), and the adopted 100% EC8 reference. With equal weights, S4 achieves the highest MCDM score (0.940) and ranks first in 95.23% of 176,851 combinations. The hypothesis that S3 would achieve the lowest WLC is not confirmed. The framework enables transparent comparison of carbon, energy, cost, and seismic trade-offs. S4’s result applies only within the quantified criteria, weighting structure, assumptions, and modelled system boundaries and does not establish universal superiority of replacement over retrofit.
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