Ontario, CA Accessory Structures: Tiny Homes (2026)

California law recognizes two distinct tiny home categories. A tiny house built on a permanent foundation to California Residential Code standards is a legal dwelling. If placed as a second unit on a single-family lot, it qualifies as an ADU under Government Code 65852.2 and must be approved ministerially in Ontario subject to the 850 to 1,000+ square-foot size rules, four-foot setbacks, and no-minimum-lot-size provisions. A tiny home on wheels (THOW) is legally either a recreational vehicle under California Vehicle Code and Health and Safety Code Division 13 Part 2.1, or a park trailer. THOWs cannot be used as a permanent residence on a standard residential lot in Ontario and cannot substitute for an ADU unless they meet state Movable Tiny House standards (HCD certification under 2020 emergency regs) and the city has adopted ordinance language to accept them. Ontario has not adopted a separate Movable Tiny House ordinance, so THOWs are treated as RVs and limited to licensed mobile home parks or RV parks. Short-term storage on a residential lot follows RV parking rules.