Substance use disorder (SUD) and posttraumatic stress disorder (PTSD) frequently co-occur and having both disorders is associated with greater psychological and functional impairment than having either disorder alone. This is especially true in residential settings where both disorders are more severe than outpatient settings. Obstructive sleep apnea (OSA) is highly comorbid with both disorders and untreated OSA is associated with worse functional impairment across multiple domains, worse quality of life, worse PTSD, higher suicidal ideation, and higher substance use and relapse rates. Treating OSA with evidence-based positive airway pressure (PAP) in Veterans with SUD/PTSD on a residential unit is a logical way to maximize treatment adherence and treatment outcomes. This study compares OSA treatment while on a SUD/PTSD residential unit to a waitlist control group. The investigators hypothesize that treating OSA on the residential unit, compared to the waitlist control, will have better functional, SUD, and PTSD outcomes.