Building insulation materials for the best trade-off between GWP and costs. An LCA-based approach across Italian climatic zones

The energy retrofit of existing residential buildings is crucial to achieve the decarbonization targets, however, identifying optimal envelope insulation solutions is a complex challenge due to the interplay between environmental impacts, economic performance, and the different building typology and climatic conditions. This study proposes an integrated parametric framework combining dynamic energy simulation, life cycle assessment, and economic evaluation to support multi-objective decision-making in insulation retrofit design. A fully automated workflow is developed by coupling MATLAB with EnergyPlus to conduct large-scale parametric simulations. Three representative residential building archetypes, i.e., apartment block, multi-family house, and single-family house are analyzed across Italian climatic zones B to E. The framework, aiming to create a comprehensive mapping of retrofit configurations, explores combinations of several design variables: vertical and roof insulation thicknesses for five insulation materials (expanded polystyrene, rock wool, glass wool, hemp, and cork). For each scenario, operational energy consumption, life-cycle global warming potential, and net present value over a 50-year service life are assessed, incorporating three possible policy incentive schemes (0%, 50%, and 70% investment subsidies). The results highlight the strong influence of building compactness and climatic conditions on both cost- and carbon-optimal insulation. Buildings with lower surface-to-volume exhibit reduced sensitivity to insulation thickness, while detached buildings show significantly higher benefits from enhanced envelope performance. Although bio-based insulation materials present lower embodied emissions, synthetic materials, e.g., expanded polystyrene often emerge as optimal solutions when considering embodied and operational impacts. Policy incentives significantly shift the Pareto-optimal solutions, improving the economic feasibility of deeper retrofit strategies.