Garage Conversion in Riverside, CA: Cost, Permits & Rules (2026)

A garage conversion is usually the lowest-cost path to an ADU in Riverside — $70,000-$140,000, versus $180,000-$320,000 for a new detached build — because the shell already exists.

Garage Conversion Cost in Riverside

Converting an existing garage in Riverside runs $70,000-$140,000. That's well under the $180,000-$320,000 typical cost of a ground-up detached ADU, because you're reusing the foundation, walls, and roof. The biggest variables are whether the slab and framing are sound, what utility/electrical upgrades are needed, and your finish level. 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.. A converted unit rents for about $1,750-$1,950/mo (1BR) in Riverside.

The Riverside Garage Conversion Permit Process

A garage-to-ADU conversion in Riverside needs building permits even if the exterior is unchanged. Approval process: Ministerial building permit, no hearing or environmental review, through the Community & Economic Development Department's One Stop Shop (3900 Main St, 3rd floor, 951-826-5800), applied for online on the Riverside Public Permit Portal. Custom designs: a plan set from a licensed design professional with site plan, floor plan, ceiling plan, elevations, cross-sections, roof, framing and foundation plans, structural details and calculations, electrical, mechanical and plumbing plans, Title 24 energy forms and, unless waived, a soils report (Building Plan Check Submittal Guidelines; new ADUs including garage conversions are project type E, JADUs type A). Planning issues a clearance, then plans route to Building & Safety, Fire, Planning, Historic Preservation, Riverside Public Utilities (electric and water) and Public Works. Permit-ready route (Dwell Riverside): 1) confirm eligibility on the ADU Express Eligibility Form (single-family lot zoned R-1, RE, RR, RC or RA-5 with an existing or proposed house; not in a flood zone, a Cultural Resources overlay, or a very high fire hazard severity zone under RMC 16.32.365; meets the grading exemption); 2) pick one of four plans and an exterior style; 3) mark the unit's location on a MapRiverside printout as a preliminary site plan; 4) complete the plan cover sheet (T1.1); 5) sign the Hold Harmless Agreement; 6) upload everything to the Permit Portal; 7) after review, download the conditions report and fee estimate, clear conditions at the One Stop Shop, pay fees and pull the permit. Qualifying lots can use the Express submittal, which the city says can reach permit issuance in as few as two One Stop Shop visits. Designated or eligible cultural resources apply for a Certificate of Appropriateness ($0 fee, staff review against the 2025 ADU Design Standards for Historic Properties) first. A permit is valid for 12 months 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. 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.

1. Confirm eligibility — 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.
2. Prepare conversion plans — layout, egress windows, insulation, ventilation, smoke/CO detectors, plus a kitchen and bathroom.
3. Submit for 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.
4. Pull permits and build — fees run 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.; then framing, electrical, plumbing, and final inspection.

No Replacement Parking Required

No. California law (AB 68 / Gov Code §66314) prohibits cities from requiring replacement parking when you convert or demolish a garage to build an ADU — so you do not need to add a parking space anywhere on the lot. Owner-occupancy is not required, so you can rent the converted unit out.

The JADU Option for an Attached Garage

If your garage is attached to the house, you can convert it into a junior ADU (JADU) — capped at 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) and built within the existing walls. JADUs are cheaper and faster to permit than a full ADU, though they may share sanitation with the main home. A full ADU gives you more size and a separate unit; a JADU is the budget route.

Riverside Garage Conversion FAQ