ADU rules in Rialto, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Rialto allows ADUs on single-family and multifamily lots under California Government Code §66314 (formerly §65852.2), with local zoning standards in Rialto Municipal Code Title 18 (Zoning). State law preempts most restrictive local provisions: a detached ADU up to 1,200 sq ft and a JADU up to 500 sq ft are allowed by right on a single-family lot, plus the city must permit at least one ADU and one JADU per single-family parcel.
Under Gov. Code §66314, Rialto must ministerially approve a permit for one ADU and one JADU on any single-family lot. Detached ADUs are capped by state law at 1,200 sq ft (a city cannot reduce this below 850 sq ft for studio/1-bedroom or 1,000 sq ft for 2+ bedroom under §66314(c)(2)(C)). Side and rear setbacks may not be required to exceed 4 feet, and no setback is required for an ADU converted from an existing structure. Maximum height is set by state default at 16 ft (detached) or 18-25 ft in certain transit/multifamily contexts. Off-street parking cannot be required if the ADU is within ½ mile of public transit, in a historic district, or part of a permitted residential conversion. Rialto's zoning (Title 18) supplies local design, fire-code (RMC Ch. 15.28), and building-permit overlays consistent with the 2022/2025 California Building Standards Code adopted by the city's Building & Safety Division.
Building without a permit can trigger stop-work orders, double permit fees, and code-enforcement citations under RMC Title 15. Unpermitted ADUs may be ordered abated or legalized; CA Health & Safety Code §17980.12 allows a 5-year delay of enforcement on substandard ADUs built before 2020 if they meet basic health/safety standards.
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