Rialto's Accessory Structures: The Rules That Matter

Every city handles accessory structures a little differently. In Rialto, California, there are 5 distinct rules that residents and property owners should be aware of. Some are stricter than what neighboring cities enforce, and others are more relaxed. Here is what you need to know.

ADU Owner Occupancy

Rialto Municipal Code Sec. 18.10.070(H) does not require an owner to live in the primary house or the accessory dwelling unit. An investor can build an ADU, keep both units as rentals, and never occupy the property. The one exception is a junior accessory dwelling unit, where owner occupancy of either the primary residence or the JADU is mandatory.

Key details: Owner occupancy: Not required for standard ADUs. JADU exception: Owner must occupy primary home or JADU. Minimum rental term: Over 30 days if rented. Governing section: RMC 18.10.070(H). Approval process: Ministerial, 60 days, no hearing.

Subsection H itself imposes no occupancy penalty because none is required for standard ADUs. The enforceable trigger is the junior ADU exception: if a JADU is built but neither the primary home nor the JADU is owner-occupied, the unit falls out of compliance with Section 18.10.070(H), and the Community Development Department can treat the structure as an unpermitted accessory building subject to zoning code enforcement and potential permit revocation.

If you are coming from a city with tighter rules, you will find Rialto gives residents more flexibility on adu owner occupancy.

ADU Rules

Rialto allows one ADU plus one junior ADU per single-family lot with ministerial approval within 60 days under Rialto Municipal Code Section 18.10.070. Detached ADUs are limited to 16 feet in height, four-foot side and rear setbacks, and 1,200 square feet maximum.

Key details: Max ADU size: 1,200 sq ft (50% of primary or 850-1,000 sq ft floor). Detached height limit: 16 feet or one story, whichever is less. Setbacks: 4 ft minimum to side and rear property lines. Review: Ministerial, no hearing, 60-day decision. Pre-approved plans: 11 city pre-selected ADU plans, 499-1,200 sq ft.

Building an ADU without permits triggers code enforcement and after-the-fact permitting; however, under AB 2533 (Government Code 66332) Rialto cannot deny a permit to legalize a unit built before January 1, 2020 unless substandard conditions exist.

The rules around adu rules in Rialto lean permissive, but that does not mean anything goes.

Garage Conversions

Rialto ministerially approves conversion of an existing, legally permitted garage into an ADU with no new setbacks and no replacement parking, but the garage door must be replaced with windows or doors matching the home. Unpermitted units built before 2020 can be legalized under AB 2533.

Key details: Approval: Ministerial; conversions keep existing setbacks. Garage door: Must be removed and replaced with matching windows/doors. Replacement parking: Not required when garage or carport is converted. Allowed expansion: Up to 150 sq ft for ingress and egress (Gov. Code 66323). Pre-2020 units: Legalization path under AB 2533 / Gov. Code 66332.

Unpermitted garage conversions are subject to code enforcement, but for units completed before January 1, 2020 the city may not penalize an applicant seeking legalization and must approve permits needed to correct health and safety violations.

Shed & Carport Rules

Rialto lists accessory buildings and gazebos among work requiring a building permit. Under Municipal Code Section 18.52.030, detached accessory buildings may occupy at most 25 percent of the rear yard and need 10 feet of separation from the house if over 120 square feet.

Key details: Rear yard coverage: Max 25% of rear yard for detached accessory buildings. Total lot coverage: Max 30% of lot area in single-family zones. Setback: May be within 5 ft of interior property lines by the rear yard. Separation: 10 ft from main house if roof area exceeds 120 sq ft. Living quarters: Accessory buildings may not be used as living quarters.

Unpermitted accessory buildings are code violations; Rialto requires permits for accessory buildings, gazebos, patios, and masonry walls, and code enforcement can require after-the-fact permits or removal. Contact Building and Safety at (909) 820-2505.

ADU Rental Restrictions

Rialto Municipal Code Sec. 18.10.070(H) sets a firm floor on accessory dwelling unit tenancies: any rental must run longer than thirty days. The rule bars ADUs from operating as short-term or vacation rentals, though it places no cap on how long a lease can run, and it applies regardless of whether the primary home or the ADU itself is rented.

Key details: Minimum rental term: More than 30 days. Short-term/vacation rentals: Not permitted for ADUs. Governing section: RMC 18.10.070(H). Applies to: Attached, detached, and converted ADUs. Enforcement: Community Development Department.

Renting an accessory dwelling unit for thirty days or less violates Section 18.10.070(H) directly. Because the city does not issue short-term rental permits for ADUs at all, unlike its separate short-term rental registration for primary dwellings, a violation here is a zoning noncompliance the Community Development Department can pursue through code enforcement, including notice to cure and referral for zoning violation proceedings rather than a fine schedule specific to short-term rentals.

The Bottom Line

Compared to many U.S. cities, Rialto gives residents more room on accessory structures. 2 of the 5 rules here are rated permissive. But permissive does not mean unregulated. There are still requirements, and the city does enforce them when violations are reported.

All of the above reflects Rialto's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.