Ontario, CA Accessory Structures: ADU Rules (2026)

Section 5.03.010 of the Ontario Development Code allows and regulates accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs) in compliance with Chapter 13 of Division 1 of Title 7 of the California Government Code (Gov. Code 66310 et seq.). An ADU that conforms to the Section is not deemed inconsistent with the City's general plan or zoning, does not exceed allowable density, and is not considered when applying any local growth-limit ordinance. ADUs and JADUs are processed ministerially; an application is approved or denied within 60 days. Detached and attached ADUs are limited to 850 square feet for a studio or one-bedroom unit and 1,000 square feet for two or more bedrooms, with attached ADUs further limited to 50 percent of the floor area of the existing primary dwelling. No size, lot-coverage, or open-space limit may require an ADU to be less than 800 square feet. A detached ADU may not exceed 16 feet in height, except up to 18 feet within one-half mile of a major transit stop or high-quality transit corridor (20 feet to match the primary roof pitch), and up to 18 feet on a lot with a multi-story multi-family dwelling; an attached ADU may not exceed 25 feet or the underlying zone height limit, whichever is lower, and cannot exceed two stories. New ADUs require minimum 4-foot rear, interior side, and street side setbacks, with front-yard setbacks following the underlying zoning district; a 6-foot separation is required between detached structures. One off-street parking space is required per ADU and may be provided in setback areas or as tandem parking, but parking is not required for ADUs meeting the state exceptions in Section 5.03.010.F.6.b. Owner-occupancy is not required for ADUs (it applies only to JADUs). ADUs may not be used as short-term rentals and may be rented only for terms of 30 days or more. Impact fees apply only to units of 750 square feet or larger.