The rapid urbanization of contemporary metropolitan areas has precipitated a significant shift in residential development, often leading to the erosion of the communal fabric that once defined neighborhood living. Within the specific context of Tehran, this evolution has frequently resulted in the proliferation of residential complexes characterized by the poor quality of shared spaces, unclear spatial boundaries, and a subsequent decline in both social interaction and perceived security among residents. The challenges posed by these environments are profound, as the lack of definition regarding the transition between the strictly private domain of the home and the broader public realm of the city creates a psychological vacuum that undermines the sense of safety. This research investigates the critical role of intermediate spaces—those transitional zones that function as bridges between private apartments and public streets—in mitigating these issues. By integrating participatory design strategies into the conceptualization and management of these spaces, it is possible to transform them from neglected voids into vibrant, socially active areas that foster security. The study employs a comprehensive mixed-methods research design, combining qualitative insights with quantitative evaluation to capture the multifaceted nature of residential life. Through the utilization of expert interviews and theoretical content analysis, the research establishes a robust conceptual framework that emphasizes the importance of design in shaping human behavior. Furthermore, the application of questionnaires, factor analysis, and structural equation modeling allows for a sophisticated examination of the relationships between environmental attributes and resident perceptions. These methodological tools are deployed to delineate the intricate connections between physical design features and the subjective experience of security, ensuring that the findings are both theoretically grounded and empirically supported. The findings of this research suggest that perceived spatial security is not merely a product of physical barriers or surveillance, but rather a dynamic outcome strongly supported by social interaction, place attachment, and the active multifunctionality of the environment. When residents feel that their intermediate spaces are designed to accommodate a variety of needs, they are more likely to maintain a consistent physical presence within those areas. This increased presence serves as a form of natural surveillance, which inherently enhances the safety of the collective environment. Moreover, the research highlights that the quality of the landscape and the intentional design of multifunctional areas serve as catalysts for social engagement. By creating environments that encourage people to linger and interact, designers can facilitate the development of place attachment, which in turn motivates residents to take an active role in the management and decision-making processes regarding their shared surroundings. The sense of belonging that arises from this participatory approach transforms the residential complex from an anonymous collection of units into a cohesive community. When residents participate in the design of their intermediate spaces, they cultivate a heightened sense of shared responsibility, which reinforces the social cohesion necessary to maintain a secure and welcoming atmosphere. The evidence gathered indicates that successful residential design must move beyond purely functional considerations to address the psychological and social needs of the inhabitants. The integration of participatory design components proves essential in bridging the gap between the private and public realms, effectively turning anonymous corridors or plazas into meaningful social hubs. This transformation is particularly vital in Tehran, where high-density living requires strategic interventions to maintain the quality of life and residential safety. By prioritizing natural surveillance through active usage and fostering a strong sense of ownership through collaboration, designers can alleviate the anxiety associated with unclear boundaries and weak spatial quality. The conclusions drawn from this investigation underscore that the path to safer residential environments lies in the empowerment of residents. When community members are involved in the spatial configuration and long-term maintenance of their living environments, the resultant social density acts as an effective deterrent to perceived threats. Furthermore, the multifunctionality of these spaces encourages spontaneous social interaction, which is the cornerstone of a resilient neighborhood. This study demonstrates that the perceived security of a residential complex is intimately tied to the social processes that the built environment enables. Ultimately, the transition from passive observation to active engagement, supported by thoughtful and inclusive design, is what guarantees the long-term sustainability and safety of contemporary residential developments. Strengthening the connection between individuals and their spatial surroundings through inclusive and deliberate design interventions proves that the revitalization of intermediate spaces is a powerful strategy for enhancing the overall residential quality of life. This academic inquiry provides a clear pathway for urban planners and architects to create environments that not only address the physical requirements of residents but also foster the psychological security and social connectivity that are fundamental to modern urban existence. The synthesis of design quality, multifunctionality, and participatory engagement emerges as a definitive framework for future residential planning, ensuring that the complexes of tomorrow are not merely housing, but truly safe and vibrant communities.