ADU Rules: Ontario vs Rialto
How do adu rules rules compare between Ontario, CA and Rialto, CA?
Rialto has fewer restrictions than Ontario.
Ontario, CA
San Bernardino County
Ontario must allow ADUs and JADUs under California Gov Code 65852.2 and 65852.22 on all single-family and most multifamily lots. Approval is ministerial within 60 days, with no minimum lot size.
View full Ontario rules →Rialto, CA
San Bernardino County
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.
View full Rialto rules →Key Facts Comparison
| Fact | Ontario | Rialto |
|---|---|---|
| State law | Gov Code 65852.2 and 65852.22 | - |
| Size | Up to 850-1,000+ sq ft detached | - |
| Setbacks | 4 ft side and rear | - |
| Parking | Waived near transit, half mile | - |
| Approval | Ministerial, 60 days | - |
| Governing law | - | Cal. Gov. Code §66314 (state ADU statute) + Rialto Municipal Code Title 18 (Zoning) |
| Max ADU size (state floor) | - | 850 sq ft studio/1-BR; 1,000 sq ft 2+ BR; up to 1,200 sq ft allowed |
| Min setback | - | 4 ft side/rear (state preemption) |
| Approval timeline | - | 60 days ministerial review (Gov. Code §66317) |
| Permit office | - | Rialto Building & Safety, 150 S Palm Ave, (909) 820-2505 |
Highlighted rows indicate differences between cities.
Ontario FAQ
Can Ontario deny my ADU application?
Only if the project fails the objective state-law or local standards. Otherwise state law requires ministerial approval within 60 days of a complete application.
Do I have to live on site to build an ADU?
No. State law suspends owner-occupancy requirements for ADUs permitted through January 1, 2025, a window that has been extended further by subsequent legislation.
Rialto FAQ
Can Rialto deny my ADU if I meet state standards?
No. State law requires ministerial (non-discretionary) approval if your ADU meets the objective standards in Gov. Code §66314 — Rialto cannot impose a public hearing or design review on a code-compliant ADU.
Do I need to live on the property to build an ADU?
No owner-occupancy is required for an ADU permitted between Jan 1, 2020 and Jan 1, 2025 under Gov. Code §66314(a)(6). JADUs always require owner-occupancy of either the main house or the JADU under Gov. Code §66333.
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