A BIM–LCA Framework for Whole-Life Carbon Assessment Under EPBD: Scope Alignment, Functional Unit Robustness, and Cross-Tool Validation

The recent revision of the European Energy Performance of Buildings Directive (EPBD) introduces mandatory whole-life global warming potential (GWP) reporting, creating practical challenges for building life-cycle assessment due to incomplete life-cycle phase coverage in conventional Environmental Product Declarations (EPDs). This study develops and validates an integrated BIM–LCA framework for structured whole-building GWP evaluation through harmonized life-cycle module alignment and cross-tool comparison, with emphasis on the early design stages. The workflow combines rapid BIM-based screening with detailed external LCA validation, establishing a tiered assessment strategy that enables iterative material optimization within the BIM environment prior to expert review. The methodology is applied to two residential construction systems (masonry and timber), and three functional units are evaluated: total whole-building GWP, area-normalized GWP, and material-level contributions. Five comparative scenarios are analyzed, including reference, nationally representative, optimized low-carbon, and European benchmark configurations. The results show progressive GWP reductions ranging from 5% to 30% across scenarios. Although substantial absolute deviations are observed between BIM-integrated and professional LCA tools, scenario-level rankings remain fully consistent across all functional units, confirming the robustness of the screening approach for comparative decision-making. Cross-tool validation focuses on an aligned embodied-carbon scope (A1–A3 plus selected end-of-life modules) to ensure screening robustness, while full whole-life LC-GWP (including B-modules and services) is positioned as the regulatory context for subsequent expert-stage assessment. The framework provides an efficient and transferable decision-support methodology that supports early-stage carbon optimization while preserving methodological transparency for regulatory reporting.