Introduction
The building sector is one of the largest energy consumers in Iran, and its mechanical and electrical systems, in addition to their direct impact on energy consumption, play a crucial role in maintaining safety, operational continuity, and the resilience of buildings during emergencies. However, existing studies have generally examined these two aspects separately. Considering the requirements of Chapters 19 and 21 of the Iranian National Building Regulations, there is a need for an integrated framework to simultaneously enhance energy efficiency and the resilience of building mechanical and electrical systems, thereby reducing energy consumption and operational costs while improving the safety and operational sustainability of buildings. The objective of this study is to develop an integrated framework for simultaneously evaluating the energy performance and resilience of mechanical and electrical systems in residential buildings, determining the optimum thickness of expanded polystyrene (EPS) thermal insulation, and prioritizing resilience enhancement strategies in accordance with the requirements of Chapters 19 and 21 of the Iranian National Building Regulations. The research seeks to answer the following questions: What is the optimum thickness of thermal insulation for reducing building energy consumption? Which factors have the greatest influence on the resilience of building mechanical and electrical systems? How can the integration of the requirements of Chapters 19 and 21 of the Iranian National Building Regulations simultaneously improve the energy efficiency and resilience of residential buildings?

Methodology
The present study is application-oriented and developmental in terms of its objective and adopts a descriptive–analytical methodology with a quantitative approach. First, previous studies, the requirements of Chapters 19 and 21 of the Iranian National Building Regulations, ASHRAE standards, and passive defense guidelines were comprehensively reviewed to identify the evaluation indicators for energy performance and resilience and to establish the research framework. Subsequently, a representative residential building was modeled, and its energy performance was simulated using Carrier HAP software under 80 different scenarios involving variations in expanded polystyrene (EPS) insulation thickness, window type, and building orientation. Thereafter, resilience enhancement strategies were prioritized using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), and a sensitivity analysis was conducted to evaluate the robustness of the results. Finally, the energy performance indicators, including annual heating and cooling loads, the overall heat transfer coefficient (U-value), the heat loss coefficient (H), the specific heat loss coefficient (H̄), and the optimum insulation thickness, were calculated. Based on the obtained results, appropriate strategies were proposed to simultaneously improve the energy efficiency and resilience of residential buildings.

Results and discussion
The energy simulation results demonstrated that increasing the thickness of EPS thermal insulation significantly reduced the building's heating and cooling loads. However, as the insulation thickness increased, the incremental energy savings gradually diminished, indicating a reduction in the marginal effectiveness of additional insulation. The results of the energy and economic analyses indicated that the optimum insulation thickness was 7–8 cm for the external walls and 5–6 cm for the roof. Compliance with the requirements of Chapter 19 of the Iranian National Building Regulations can reduce building energy consumption by approximately 25–40%. Furthermore, the resilience assessment revealed that emergency power supply, equipment redundancy, fire detection and suppression systems, emergency ventilation, and safe shelter facilities are among the most critical factors contributing to the resilience of building mechanical and electrical systems. The weighting of the evaluation criteria using the Best–Worst Method (BWM) and the prioritization of resilience enhancement strategies using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) indicated that upgrading critical systems and ensuring the availability of backup resources have the greatest impact on improving building resilience. Overall, the integration of the requirements of Chapters 19 and 21 of the Iranian National Building Regulations provides a comprehensive and effective framework for simultaneously enhancing energy efficiency, reducing operational costs, and improving the resilience of residential buildings.

Conclusion
The results of the resilience assessment indicated that the mechanical and electrical systems play the most significant role in enhancing building resilience. Furthermore, measures such as providing an emergency power supply, increasing the redundancy of critical equipment, and improving safe shelter facilities were identified as the most effective strategies for enhancing building resilience. Furthermore, the energy simulation results demonstrated that the combined application of double-glazed windows and expanded polystyrene (EPS) thermal insulation significantly reduced heat loss and annual heating and cooling loads. Moreover, compliance with the requirements of Chapter 19 of the Iranian National Building Regulations can result in energy savings of approximately 25–40%. Based on the technical and economic analyses, the optimum insulation thickness was determined to be 7–8 cm for the external walls and 5–6 cm for the floor above the parking area. The main contribution of this study is the development of an integrated framework for the simultaneous evaluation of building energy performance and resilience through the combined use of energy simulation and the Best–Worst Method (BWM) and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS), which enables more effective decision-making for the design of sustainable and resilient residential buildings. The proposed framework can serve as an effective decision-support tool for the design of sustainable, energy-efficient, and resilient residential buildings. Furthermore, it provides a robust foundation for future research aimed at extending this approach to other climatic regions and diverse building typologies.