ABSTRACT People with serious mental illness (SMI) experience dramatically worse health and longevity than the general population, which is exacerbated by extremely high rates of loneliness and social isolation. Both social isolation (lack of social supports) and loneliness (the subjective experience of isolation) are highly predictive of early mortality. Although social isolation and loneliness are inherently relational, influenced by contextual factors, and prevalent among people with SMI, very little is known about how to design community mental health environments that foster social connection (“social architecture”). Thus, the goal of this K01 is to lay the foundation for an innovative, impactful research career focused on reducing social isolation among people with SMI through environmental design. My research plan employs a rigorous, mixed-method design to: 1) identify environmental features associated with two behavioral mechanisms of action: activity engagement and social interaction; 2) examine associations between activity engagement, social interaction, and self-reported loneliness and support; and 3) feasibility test the co-design and implementation of an environmental modification to support social connection. To do this, I will first conduct socio-spatial observations of activity engagement and social interaction in four mental health Clubhouses in Hawaii. These are community-based psychosocial rehabilitation centers that are highly interested in reducing loneliness among their members. Observation data will be paired with survey data (N=150) to examine associations between observed activity engagement and social interaction and self-reported loneliness and social support. Second, spatial observations and social network data will be visualized to refine a conceptual model interlinking engagement and social interaction. These visualizations will be shared with participating Clubhouses to contextualize the identified patterns in engagement and social interaction and to co-identify potentially modifiable environmental features associated with them. Third, an environmental intervention co-design process will be conducted in one Clubhouse and the intervention will be implemented. Feasibility data on the co-design process and modification of the environmental intervention protocol will be collected through field notes and a final focus group and subsequently analyzed qualitatively. This research will be carried out with close mentorship from a team of highly accomplished senior scholars: Drs. Henwood, Wenzel, Salzer, Valente, Wilson, and Stark. Their work is directly aligned with my career and training goals, which focus on three intersecting areas of expertise: 1) socio-spatial methods (GIS, social network analysis and ecological momentary assessment), 2) theory linking environmental design, human behaviors, and health, and 3) environmental intervention co-design based on community-based participatory research principles. This K01 build...