ADU rules in Riverside County

Detached ADUs are permitted by right in unincorporated Riverside County on any lot zoned for single-family use, or in any zoning classification that permits a one-family dwelling, that holds or will hold a single-family home, and on multifamily lots (Ord. 348 § 19.802.A, as rewritten by Ord. 348.5056, in effect since October 15, 2026). A single-family lot may carry one new attached or detached ADU plus a conversion ADU, and units may be combined in any quantity state law allows, such as one detached ADU, one conversion ADU and one JADU (19.802.D.1). A lot with an existing multifamily building may add up to eight detached ADUs (never more than its existing unit count) and a lot with a proposed one up to two (19.802.D.2.a, tracking Gov. Code 66323(a)(4)). A detached ADU may be a manufactured home, and the old code's bars on lots with unpermitted dwellings or constrained water or sewer service are gone.

Attached ADUs (one per single-family lot, with its own exterior entrance; interior access to the main home is allowed) and conversion ADUs within the existing or proposed space of a home or accessory structure are permitted (Ord. 348 §§ 19.802.D.1, 19.802.J). A conversion ADU may add up to 150 sq ft beyond the existing structure for access (19.802.E.3.c). On multifamily lots, conversion ADUs may be built in non-livable space such as storage rooms, attics, basements or garages, up to 25 percent of the existing units and never fewer than one (19.802.D.2.b). A JADU of up to 500 sq ft of interior livable space fits entirely inside a single-family home (an attached garage counts as part of the home), one per lot, and is not allowed on multifamily lots (19.803.A, D).

"A detached ADU established on a lot containing an existing or proposed single-family dwelling shall be not exceed one thousand six hundred (1,600) square feet of floor area," and an attached ADU "shall not exceed 50 percent (50%) of the floor area of the existing primary dwelling or one thousand six hundred (1,600) square feet of floor area, whichever is less," though the 50 percent rule never blocks an attached ADU of at least 1,000 sq ft (Ord. 348 § 19.802.E.3). Detached ADUs on multifamily lots follow Gov. Code 66323(a)(4) with no county size cap, every ADU must be at least 150 sq ft, and a JADU is 150 to 500 sq ft of interior livable space (19.802.E.2, 19.803.E). Detached ADUs may be 16 feet tall, or 18 feet on a lot with a multistory multifamily building or within half a mile walking distance of a major transit stop (plus 2 feet to match the main roof pitch); attached ADUs may be 25 feet or the zone height, whichever is less, and no more than two stories (19.802.F). The state-exempt pathway still guarantees an 800 sq ft detached unit with 4-foot side and rear setbacks regardless of these caps (Gov. Code 66323(a)(2)).

"Property owners shall not be required to occupy, or reside within, either the primary dwelling or ADU located on the same lot" (Ord. 348 § 19.802.B, effective October 15, 2026), matching Gov. Code 66315; the 2020 code's owner-occupancy rule for ADUs permitted after June 1, 2025 is repealed. JADUs are the exception: where a JADU shares sanitation facilities with the main home, the owner must live in the home or the JADU as a principal residence unless state law exempts the owner (19.803.B.1; Gov. Code 66333(b)), and a deed restriction barring separate sale of the JADU is recorded before final building permit (19.803.C.2). The county's second units no longer require owner occupancy either (19.805.B.1).

The county requires "One (1) parking space per ADU or per bedroom within the ADU, whichever is less," which may be tandem on an existing driveway or in a side or rear setback (Ord. 348 § 19.802.I.1-2). No parking or replacement parking is required for an ADU within half a mile walking distance of public transit, in an architecturally and historically significant historic district, within a proposed or existing primary residence or accessory structure, where on-street parking permits are required but not offered to the occupant, or applied for together with a new home when another exemption applies, and a garage, carport or space demolished or converted for an ADU need not be replaced (19.802.I.3). JADUs need no parking (19.803.H). The ordinance omits the state's car-share exemption, which still applies within one block of a car share vehicle through Gov. Code 66322(a)(5) and the ordinance's own rule that state law prevails (19.801.B.2.a).

"Applications for an Additional Residential Accommodation shall be reviewed and processed ministerially," and the Planning Director or designee "shall approve an application upon determining that the proposed development complies with the objective requirements of this Article" and state law, following the Gov. Code 66317 and 66335 timelines (Ord. 348 § 19.809.A): a completeness decision within 15 business days and approval or denial within 60 days of a complete application, with no hearing. Clearances from Environmental Health (septic systems and wells), water and sewer providers, Flood Control, the Airport Land Use Commission and Fire are checked within that ministerial review and need no separate discretionary entitlement (19.809.B). Unpermitted ADUs and JADUs built before 2020 can be legalized under Gov. Code 66311.7 (19.809.C). Building and Safety offers free permit-ready ADU plans of 499, 625, 749 and 909 sq ft for eligible single-family lots.

"An Accessory Dwelling Unit may be rented separately from the primary dwelling," but may not be sold or conveyed separately except as state law requires, such as the Gov. Code 66341 qualified-nonprofit path; the county has not opted into Gov. Code 66342 ADU condominiums (Ord. 348 § 19.802.C). The rewritten article sets no minimum rental term for ADUs, while "A JADU shall not be rented for periods of less than thirty (30) days" (19.803.B.3), and state law requires terms longer than 30 days for JADUs and for ADUs approved under the state-exempt pathway (Gov. Code 66323(e), 66333(g)). The county's short-term rental ordinance (Ord. 927.3, effective September 24, 2026) says a short-term rental "may include any accessory dwelling unit (ADU), junior ADU, second unit, guest quarter, or ranchet unit not otherwise prohibited by state law" but excludes units under "other legal requirements prohibiting this type of rental," so a county-standards ADU appears eligible for an annually renewed STR certificate, subject to occupancy and parking limits, the 500-certificate cap in Idyllwild and Pine Cove, the Temecula Valley Wine Country caps, and one certificate per lot where a lot holds several dwellings. Confirm STR eligibility with the Planning Department before booking short stays.