Energy-efficient retrofit of existing residential buildings is essential for reducing heating energy demand and carbon emissions in severe cold regions. However, the absence of a structured quantitative evaluation approach often limits effective decision-making in practice. This study develops a multi-dimensional evaluation framework integrating the Fuzzy Delphi Method and Analytic Hierarchy Process (AHP) to assess and prioritize building envelope retrofit strategies. A representative non-energy-efficient residential building in Changchun, China, is selected as a case study. Based on expert consultation, a hierarchical indicator system is established, and indicator weights are determined with satisfactory consistency (CR < 0.1). The results indicate that envelope thermal performance and energy–carbon benefits are the dominant factors influencing retrofit decisions. At the parameter level, insulation thermal conductivity and external wall heat transfer coefficient are identified as the most critical variables. The findings suggest that prioritizing improvements in envelope thermal performance can effectively enhance energy-saving and carbon-reduction performance under practical constraints. The proposed framework provides a practical and transferable decision-support tool for energy-efficient retrofit planning for existing residential buildings in severe cold regions.

Energy-efficient retrofit of existing residential buildings is widely recognized as a cost-effective pathway for reducing heating energy demand and carbon emissions in severe cold regions. However, retrofit decision-making in practice is often constrained by the absence of a structured and quantitative approach for evaluating and comparing the comprehensive benefits of alternative envelope retrofit strategies. In Northeast China, where a large stock of existing residential buildings is characterized by long heating seasons and insufficient envelope thermal performance, this limitation frequently leads to suboptimal retrofit prioritization. To address this gap, this study proposes a multi-dimensional decision-support framework for quantifying and prioritizing the benefits of energy-efficient envelope retrofits in existing residential buildings located in severe cold regions. A representative non-energy-efficient residential building constructed in the 1980s in Changchun, Jilin Province, is selected as a case study. Based on a systematic literature review and expert consultation using the Fuzzy Delphi Method, a hierarchical evaluation framework comprising five evaluation dimensions, twenty-four criteria, and one hundred and ten evaluation factors is established. The Analytic Hierarchy Process (AHP) is then applied to derive the relative importance of the evaluation elements and to examine the consistency of expert judgments. The results indicate that improvement of envelope thermal performance and energy and carbon emission benefits are identified as the most critical dimensions influencing retrofit decisions in severe cold regions. At the factor level, thermal conductivity of insulation materials and external wall heat transfer coefficient emerge as the most influential contributors to overall retrofit benefits. All judgment matrices satisfy the consistency requirement (CR < 0.1), confirming the reliability of the weighting results.Overall, the findings demonstrate that the proposed framework enables a quantitative and comparative assessment of retrofit benefits, supporting the prioritization of envelope retrofit strategies that simultaneously enhance thermal performance and maximize energy and carbon reduction outcomes under technical feasibility constraints. The framework provides a transferable decision-support tool for practitioners and policymakers seeking to improve the effectiveness of energy-efficient retrofit planning for existing residential buildings in severe cold climates.

It is a common phenomenon that the stairs of modern historical brick–timber buildings cannot meet existing fire protection specifications, something which has become a difficulty in their renovation. In response, this study proposes two different renovation strategies for the Hui-shaped Chinese Baroque brick–timber building in Harbin and constructs multiple fire scenarios. Using a coupled PyroSim–Pathfinder (version 2023.2.0816) simulation approach, a finite element model of the building under fire and a corresponding evacuation model are established. The aim is to investigate how variations in stair width, number, position, and overall building scale under the two renovation strategies influence evacuation movement time and the number of evacuation failures, and to compare the effectiveness of common fire protection measures. The results show that, for the same stair configuration and building mass, the fire development patterns of the two renovation strategies are similar. Increasing the stair width from the original 0.9 m to 1.1 m produces no significant improvement in evacuation performance. When the number of indoor existing stairways increases from one to two, the proportion of occupants evacuated safely rises from 68% to 91%. External corridor staircases provide the best evacuation performance, and a single such stair can satisfy the safe evacuation of all occupants. When the same additional floor area is provided, increasing the number of storeys extends the evacuation movement time by approximately twice that caused by increasing the building footprint. Automatic sprinkler systems and mechanical smoke exhaust systems exhibit more pronounced fire protection effects.