The shift in modern warfare paradigms, focusing on population centers and vital urban hubs, has significantly increased the vulnerability of cities to military attacks. Experiences from contemporary wars, particularly the eight-year Sacred Defense, indicate a rise in civilian casualties and the destruction of urban infrastructure due to advancements in military weaponry. Concurrent with these threats, accelerating population growth and limited spatial resources have highlighted the necessity for the optimal and multi-purpose utilization of underground spaces. The present study aims to define and categorize the design requirements for multi-purpose underground spaces in residential complexes. This research, employing a mixed-methods approach that includes documentary studies, content analysis, and the survey analysis of quantitative and qualitative data from a population of experts in passive defense and urban design, has identified key requirements. The results indicate that these requirements can be categorized into five main dimensions: Spatial-Functional, Infrastructural-Technical, Service-Support, Sensory-Psychological, and Safety-Access. Key components highlighted include modular design with prefabricated elements, self-sufficient HVAC systems, the design of safe and multiple access routes, standard human-centric lighting, and the provision of emergency facilities. Furthermore, the innovation of this research lies in statistically proving the importance of creating a sense of security and psychological tranquility in crisis situations—a critical and frequently overlooked requirement. The findings of this paper can serve as a valuable guide for policymakers, urban designers, and engineers in enhancing urban resilience and the efficiency of underground spaces within national housing projects and other urban development initiatives.
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