How Much Does an ADU Cost in Riverside, CA?

Construction Cost Breakdown

Building an ADU in Riverside costs between $180,000-$320,000 for new construction, with per-square-foot costs averaging $180-$280. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $70,000-$140,000, while prefab/modular ADUs fall in between at $120,000-$250,000.

Permit Costs & Timeline

Permit fees in Riverside are 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.. The review timeline is 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)., with 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. Impact fees are None on an ADU of 750 sq ft or less of interior livable space or a JADU of 500 sq ft or less (Gov. Code 66311.5(c)); RMC 19.442.030(K) mirrors the exemption (its wording omits the 'or less', so a unit at exactly 750 sq ft should cite the state threshold) and charges larger ADUs proportionately to the primary dwelling's floor area. An ADU is not a new residential use for utility connection or capacity charges unless built with a new house, an ADU inside the existing house pays no new connection fee, and a new detached ADU may pay a connection fee or capacity charge proportionate to its size or fixture count (19.442.030(J)). Separate electric, water, gas and sewer connections are optional and cost more (Riverside Public Utilities: 951-826-5489 electric, 951-826-5285 water). School district developer fees can apply to units of 500 sq ft or more. Pre-approved plans: 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.

Rental Income & ROI

A typical ADU in Riverside generates approximately $22,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $250,000, the estimated payback period is 11.3 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Riverside and varies by market (often less than build cost).

Ways to Reduce ADU Costs in Riverside