A life-cycle multi-criteria decision framework for sustainable retrofit of aging residential communities

Aging residential communities are critical targets for urban stock renewal and the low-carbon transition of the building sector. However, decision-making regarding their retrofit often involves multiple trade-offs among carbon reduction benefits, economic costs, and social impacts. To enhance the scientific validity and operability of selecting retrofit schemes, this study proposes a multi-criteria decision-making (MCDM) framework based on a life-cycle perspective. The framework first identifies feasible candidate retrofit measures and quantifies their annualized life-cycle carbon reduction, annualized life-cycle cost, and social impacts. Subsequently, through indicator normalization and weight assignment, the integrated evaluation scores of individual retrofit measures are calculated. Finally, under budget constraints and minimum carbon reduction requirements, a 0–1 combinatorial optimization model is employed to screen optimal retrofit schemes across different scenarios. Taking the Yongxing Road Community in Jinan, Shandong Province, as a case study, 13 building- and site-related retrofit measures are evaluated. The results indicate that the solar water heating system achieves the highest integrated score, followed by roof and external wall retrofits, demonstrating the high comprehensive value of renewable energy utilization and building envelope energy-saving upgrades. Under four budget scenarios, the annual carbon reduction of the optimal schemes ranges from 279.91 to 375.64 tCO₂/a, all significantly exceeding the minimum carbon reduction constraint. Sensitivity analysis reveals that the optimal schemes remain stable under various weight perturbations, indicating the robust nature of the model. Furthermore, this study categorizes the optimization results into four progressive retrofit patterns: low-cost energy-saving baseline, site function improvement, building energy enhancement, and comprehensive full-scale upgrade. These patterns provide a quantitative decision-making basis for the phased implementation of sustainable retrofits in aging residential communities.