Cannabis legalization threatens to undermine clean indoor air norms. We investigated the prevalence and nature of tobacco and cannabis use rules in Airbnb venues in Denver, Colorado, where recreational cannabis was legalized in 2014. The study used publicly available Inside Airbnb data for all Denver listings (N = 4,511) collected on 06/29/2019. We analyzed reported tobacco smoking and cannabis use house rules. Tobacco smoking with or without conditions was allowed in 9.7% of venues. Of all venues, 23.7% included details about cannabis use. Of these, 75.9% allowed cannabis use without or with conditions. Of the venues that allowed cannabis use, 30.5% also allowed tobacco smoking. Of the venues that did not allow cannabis use, 0.4% allowed tobacco smoking. Additional multilevel regression models revealed that venues in higher income neighborhoods were less likely to allow cannabis and tobacco use. A substantial number of Airbnb listings in Denver, Colorado permit cannabis use and venues permitting cannabis use may be more likely to also permit tobacco smoking. Findings support the idea that cannabis legalization threatens clean indoor air norms. Airbnb should consider including cannabis use in house rules in jurisdictions that have legalized cannabis to help guests identify spaces with clean air.