Everything homeowners ask about building an ADU in Riverside — answered with 2026 data.
Yes, ADUs are allowed in All residential zones and all multifamily and mixed-use zones with an existing or proposed dwelling (RMC 19.442.020). Permitted-use Table 19.150.020.A lists ADUs and JADUs as permitted (P) in the RC, RA-5, RR, RE, R-1, R-3, R-4, MU-N, MU-V and MU-U zones and not in the O, CR, CG, CRC, BMP, I, AI, AIR, PF and RWY zones. JADUs only on lots with a single-family home. Designated or eligible cultural resources and historic-district lots also need a Certificate of Appropriateness under Title 20 and must follow the 2025 ADU Design Standards for Historic Properties; MADUs are barred there in Riverside, CA. The maximum size for a detached ADU is 1,200 sq ft of floor area (RMC 19.442.030(D)(2)). A movable ADU (MADU, a unit on a chassis) must be 150-430 sq ft measured to the outside of the exterior walls (D)(3). Any ADU must be at least the size of an efficiency dwelling unit under California Building Code 1208.4 (D)(5). ADU floor area is not counted toward lot coverage (A)(8). Attached ADUs can be up to 50% of the existing or proposed primary dwelling's floor area or 1,200 sq ft, whichever is less, including converted floor area; the 50% cap can never block an ADU of 850 sq ft. Riverside has an ADU-friendliness score of 8/10. Check our full Riverside ADU rules page for complete zoning details.
ADU construction in Riverside typically costs $180,000-$320,000. The cost per square foot averages $180-$280. Garage conversions are more affordable at $70,000-$140,000, while prefab ADUs cost $120,000-$250,000. Permit fees add Valuation-based, not flat: roughly $1,400-$1,500 in Building & Safety permit and plan-check fees for an 800 sq ft ADU on the FY2023-24 schedule ($100.04/sq ft valuation), plus Planning's $289 zoning check and surcharges; the city's 2022 workshop put all-in fees at $3,000-$9,000. to your budget. See our detailed Riverside ADU cost guide.
Detached ADUs in Riverside can be up to 1,200 sq ft of floor area. Attached ADUs are limited to 50% of the existing or proposed primary dwelling's floor area or 1,200 sq ft, whichever is less, including converted floor area; the 50% cap can never block an ADU of 850 sq ft. Junior ADUs (JADUs) have a cap of 500 sq ft, built entirely within the walls of the existing or proposed single-family house (an attached garage counts as inside the walls), with its own exterior entrance, an efficiency kitchen, and either its own bathroom or a shared one with the main house (RMC 19.442.030(B)(5), (D)(4); Gov. Code 66333). Maximum height is Detached one-story ADU or MADU: 20 ft. Two-story detached ADU, or an ADU on the second floor of an existing accessory building: 30 ft (RMC 19.442.030(G); the city's ADU FAQ says the same). Attached ADU: the underlying zone's height limit, which is 35 ft and two stories in the R-1, RR, RE and RA-5 zones (Residential Zones handout A8). In the RC (Residential Conservation) zone any detached ADU is limited to 20 ft and one story. These exceed the state minimums of 16 ft (18 ft within a half mile of a major transit stop, plus 2 ft for a matching roof pitch) for detached and 25 ft for attached ADUs (Gov. Code 66321(b)(4)). You are allowed up to Single-family lot: the main house plus one attached or converted ADU, one detached new-construction ADU or MADU, and one JADU on a qualifying lot.
Rear setback: 4 ft for a new one-story ADU or MADU up to 16 ft tall, measured from the rear lot line and from other buildings; a taller or two-story new ADU, or a new second story added to an existing structure, must meet the base zone's rear setback (RMC 19.442.030(C); city ADU FAQ). No added setback for converting an existing structure or an existing second story. State law caps side and rear setbacks at 4 ft for any new ADU (Gov. Code 66314(d)(7)) and guarantees a detached ADU of at least 800 sq ft with 4-ft setbacks at 16 ft (18 ft near major transit), so ask the Planning Division before assuming a larger setback applies to a taller unit. Side setback: 4 ft for a new one-story ADU or MADU up to 16 ft tall; above 16 ft or for a second-floor ADU in a new structure, the base zone's side setback applies (RMC 19.442.030(C)(2)). Street-side setbacks follow the base zone. Conversions of existing structures need no additional setback, and the setback must always be enough for fire and safety access (C)(3). Front setback: A new ADU or MADU must meet the base zone's front and street-side setbacks (RMC 19.442.030(C)(2)(b)): 20 ft in R-1-7000, 25 ft in R-1-8500, R-1-10500 and R-1-13000, 30 ft in R-1-1/2 acre, RE, RR and RC, and 40 ft in RA-5 (Residential Zones handout A8). ADUs are not allowed in the front yard, and a MADU may not sit between the house and the street (B)(2). Conversions inside the existing house or an existing accessory structure keep their current setbacks, and a front setback cannot be used to block an 800 sq ft ADU with 4-ft side and rear setbacks (Gov. Code 66321(b)(3)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None. No parking space is required for an ADU, MADU or JADU, and no replacement parking is required for the main house when a garage, carport or covered parking is converted to an ADU (RMC 19.442.030(H)). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required for an ADU or MADU on a lot with the primary home (RMC 19.442.030(F)(a)). For a JADU the city code requires the owner to live in either the main house or the JADU and to record a deed restriction; since January 1, 2026 state law (Gov. Code 66333(b), AB 1154) allows that requirement only when the JADU shares a bathroom with the main house, so a JADU with its own bathroom should be exempt: confirm with the Planning Division. Every JADU needs a recorded deed restriction barring separate sale (A)(10). Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Riverside is typically Permit-ready plans: 3 business days for the first review, 10 for rechecks. Custom ADUs (Tier 2): 20 working days first review, 10 for resubmittals; paid expedited review can halve that. State law: complete applications decided within 60 days (Gov. Code 66317, SB 543). Plan check: Electronic plan check through the Public Permit Portal; each reviewing department posts its conditions in a report you download from the portal, and a plan check expires one year after fees are paid (Plan Check FAQs). Fire sprinklers are not required in an ADU or JADU unless the main house has them; a MADU needs no sprinklers but must be built to ANSI A119.5 or NFPA 1192 (RMC 19.442.030(L)). A MADU must meet the movable-ADU definition in RMC 19.910, be connected to water, sewer and electric, sit on a paved pad with its wheels and hitch screened, keep mechanical equipment off the roof and match the main house's roof pitch and materials (19.442.030(I)-(J)). Fire sprinklers and solar photovoltaics are handled as deferred submittals on the permit-ready plan sets; a two-story custom ADU needs its own structural calculations. Pre-approved plans availability: Yes. Dwell Riverside offers four free permit-ready detached single-story ADU plan sets prepared for the city: 746 sq ft (1 bed/1 bath), 800 sq ft (2 bed/2 bath), 1,020 sq ft (2 bed/2 bath) and 1,200 sq ft (3 bed/2 bath), each in Craftsman, Ranch or Spanish exteriors, with foundation options for all soil conditions and optional Very High Fire Hazard Severity Zone and noise-attenuation details. To qualify (ADU Express Eligibility Form, rev. Sept 2024) the lot must be single-family (R-1, RE, RR, RC or RA-5), outside a flood zone, outside the Cultural Resources overlay, outside a very high fire hazard severity zone (RMC 16.32.365) and meet the grading exemption; you sign a hold-harmless agreement and complete the T1.1 cover sheet. Presented to the City Council on December 10, 2024; the city had permitted 835 ADUs and JADUs from 2019 through September 2024.
Average ADU rental income in Riverside: 1-bedroom units rent for $1,750-$1,950/month, 2-bedroom units for $2,200-$2,400/month. Short-term rentals: No. Expected ROI: About 7-12% gross rental yield on a $180,000-$320,000 detached build at $1,750-$1,950/mo, before taxes, vacancy and financing; a $70,000-$140,000 garage conversion at the same rent returns roughly 15-30% gross.
The minimum lot size for an ADU in Riverside is No minimum lot size to establish an ADU, MADU or JADU (RMC 19.442.030(A)(7)), and the city cannot require you to fix existing zoning nonconformities first (A)(6). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Riverside, a garage conversion typically costs $70,000-$140,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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