Introduction. Comprehensive smoke-free policies are effective in reducing secondhand smoke (SHS) exposure, but they do not protect residents in multi-unit housing. Recent cannabis legalization in California has increased exposure to secondhand cannabis smoke in multi-unit housing. We applied the Capability, Opportunity, Motivation, Behavior (COM-B) model, a theory-informed set of strategies for understanding barriers to and enablers of behaviors associated with indoor smoke exposure in San Francisco’s Section 8 federally subsidized housing.

Methods. In partnership with the San Francisco Housing Authority we conducted focus groups (n=17 focus groups) with residents and in-depth, semi-structured interviews with housing staff representing 16 out of 30 housing sites. We analyzed transcripts using the COM-B model.

Results. Of the 134 residents, 50% were black or Latinx and 29% smoked currently. Among smokers, 27% concurrently used cannabis in the past 30 days. Of the 27 staff, 66.7% were black or Latinx and 18% smoked currently. Residents did not experience barriers to smoking outside their home (physical Capability), but experienced benefits from smoking such as stress relief, that affected their ability to self-regulate (psychological Capability). Staff lacked the psychological Capability to discuss the impacts of SHS on residents’ health. Physical and social Opportunity, including a lack of a safe space to smoke outdoors and the normalization of indoor cannabis use supported residents’ preference for indoor smoking. Minimizing exposure to all forms of SHS among pets and children was a Motivation for residents to not smoke indoors. Staff reported lacking Motivation to enforce an indoor no-smoking rule because a strong belief that eviction should not be a repercussion of policy violation.

Conclusion. Interventions to promote smoke-free living in multi-unit housing should target all combustible tobacco, nicotine and cannabis products, and include ways to address motivations so that residents voluntarily adopt smoke-free homes.