wseas-12059-20260917123324-6907eb 20260917123324076 wseas/wseas wseas.group@gmail.com WSEAS WSEAS Transactions on Heat and Mass Transfer 1790-5044 2224-3461 05 25 2026 05 25 2026 21 Carmela Concilio Department of Civil Engineering, University of Salerno, Via Giovanni Paolo II, 132, Fisciano, I-84084, ITALY Vincenzo M. La Rocca Department of Physics, University of Salerno, Via Giovanni Paolo II, 132, Fisciano, I-84084, ITALY Giuseppe Vicidomini Department of Physics, University of Salerno, Via Giovanni Paolo II, 132, Fisciano, I-84084, ITALY Gennaro Cuccurullo DepartmDepartment of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, Fisciano, I-84084, ITALYent of Physics, University of Salerno, Via Giovanni Paolo II, 132, Fisciano, I-84084, ITALY Deep renovation of existing buildings is commonly planned according to the Fabric-First principle, with envelope improvements preceding heating-system upgrades. This study assesses whether a different ordering of the same retrofit measures can provide better intermediate energy and economic outcomes. Two cumulative trajectories are compared: a conventional Fabric-First sequence and a Low- Invasiveness-First sequence, in which system upgrades precede extensive insulation works. The analysis uses a coupled 0D–1D dynamic building–plant model, combining lumped energy balances for indoor zones and heating emitters with one-dimensional transient heat conduction through envelope components, driven by hourly Typical Meteorological Year data. The method is applied to a representative 1970s Italian apartment building in Salerno and Tolmezzo, representing mild Mediterranean and cold Alpine climates. Seasonal heating demand, operating expenditure, capital cost, and marginal cost-effectiveness are evaluated for each cumulative package. Both trajectories reach the same final configuration, but their intermediate performance differs. The Low-Invasiveness-First sequence generally yields lower operating costs at low and medium investment levels, especially in Salerno. Once the complete package is implemented, operating costs decrease by more than 70% in both locations. The results showthat retrofit sequencing can materially affect the timing and cost-effectiveness of renovation benefits. 09 17 2026 09 17 2026 88 9 https://creativecommons.org/licenses/by/4.0/ 10.37394/232012.2026.21.9 https://wseas.com/journals/articles.php?id=12059 N. Eyre, T. Fawcett, M. Topouzi, G. Killip, T. Oreszczyn, K. Jenkinson, and J. Rosenow, “Fabric first: is it still the right approach?” Buildings and Cities, vol. 4, no. 1, pp. 965–972, 2023. [Online]. 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