ADU Builder in Riverside, CA: Permit-Ready Plans, Permits and Costs

What are the size, height and yard rules for an ADU in Riverside?

Riverside allows an ADU on any lot with an existing or planned primary dwelling, in the side and rear yards only, and the first floor must sit at least four feet from all property lines and from other buildings. A second floor cannot sit in that setback. A detached ADU may reach 1,200 square feet of livable space, and an attached ADU may reach 1,200 square feet or 50 percent of the primary dwelling, whichever is less. The city's own FAQ says at least 850 square feet is allowed in every case, so a 2,000 square foot house can take a 1,000 square foot attached unit. In most areas of the city the height limit is 35 feet attached and 30 feet detached, and two stories are usually allowed.

How long does Riverside take to review and approve an ADU permit?

California law gives the city 15 business days to issue a written notice on whether an ADU application is complete, then 60 days from receipt of a complete application to approve or deny it. Under Section 66317(a)(3) an application the city has not acted on within 60 days is deemed approved. Riverside's own permit-ready plan route is quicker than a custom submission: the city publishes a 3 business day turnaround for the initial plan review of its pre-approved ADU plans, and 10 business days for any later plan review. The city takes these applications through its Public Permit Portal.

What fees does the City of Riverside charge for an ADU?

Every ADU in Riverside pays plan check and permit issuance fees, and the city says ADUs are also subject to some but not all of the development impact fees and utility connection capacity fees that primary dwellings pay. The city's Planning Division publishes a fee schedule covering single-family residential work including accessory structures. State law sets the impact fee floor: under Section 66311.5(c)(1) no impact fee can be charged on an ADU of 750 square feet of interior livable space or less, or a JADU of 500 square feet or less, and any fee above that threshold is charged in proportion to the primary dwelling's square footage. Riverside offers no financial assistance for ADU construction, though the state may have grants of up to $25,000.

How much does an ADU cost in Riverside?

L Square's configured prefab model prices are $180,000 for Model 600, $240,000 for Models 800A and 800B, $295,000 for Models 1000A and 1000B, and $354,000 for Model 1200. These are model prices, not final project totals. Riverside lots carry their own costs, including utility capacity, sewer or septic work, foundation conditions and slope. The city's pre-reviewed plans can cut architecture and engineering cost before drawings are priced, and an ADU may have separate water, electricity, gas, sewer and telecom connections or share the services of the primary dwelling.

What should I check before I build an ADU on a Riverside lot?

Start with the zoning of the lot. Riverside's permit-ready plan catalogue applies only to single-family residential zoned sites in the R-1, RE, RR, RC and RA-5 districts, to sites outside a flood hazard area, and to sites that are not designated or eligible for designation as a cultural resource under Title 20 of the Riverside Municipal Code. Historic property owners have a separate path: the city adopted Design Standards for Accessory Dwelling Units on Historic Properties on February 19, 2025, and ADU work on those lots is reviewed under Chapter 19.442 of the Riverside Municipal Code. Check utility service early, since a separate meter or a new sewer lateral changes both the price and the schedule.

Official Riverside ADU sources

• The City of Riverside publishes four single-story permit-ready ADU plan types: 746 square feet with 1 bedroom and 1 bathroom, 800 square feet with 2 bedrooms and 2 bathrooms, 1020 square feet with 2 bedrooms and 2 bathrooms, and 1200 square feet with 3 bedrooms and 2 bathrooms, each in Craftsman, Ranch and Spanish styles. To use them the site must be zoned single-family residential (R-1, RE, RR, RC, RA-5), outside a Flood Hazard Area, and not a Cultural Resource under Title 20 of the Riverside Municipal Code. The city states a 3 business day initial plan review. Official source
• The city's Dwell Riverside program gives applicants two paths: custom plans prepared by a licensed professional, or permit-ready plans that are pre-reviewed and customizable for a faster and more cost-effective process. The city says pre-review by the Building Division can help reduce preconstruction architecture and engineering costs, and that both options go through the standard building permit review process. Official source
• The City's ADU FAQ, revised March 2022, says a detached ADU may be up to 1,200 square feet of livable space and an attached ADU may be up to either 1,200 square feet or 50% of the size of the primary dwelling, whichever is less, and that in every case at least 850 square feet is allowed, so a 2,000 square foot house may have an attached ADU of up to 1,000 square feet. It also says ADUs are allowed in the side and rear yards but not in front yards, and that the state may have grants of up to $25,000. Official source
• The City's earlier Accessory Dwelling Units FAQ says ADUs may be constructed on any lot developed with an existing primary dwelling or where one will be built at the same time, that ADUs may be attached or detached, that they are allowed in the side and rear yards but not in front yards, and that in the side and rear yards they must be set back at least four feet from all property lines and from other buildings. It says ADUs do not require any additional parking. Official source
• The City's Safety-First Amnesty Program says Senate Bill 1226 was signed into law on September 30, 2018 and was codified into the Health and Safety Code to address unpermitted residential dwellings, and that Assembly Bill 2533 was signed into law on September 28, 2024 and is specifically applicable to ADUs and JADUs. AB 2533 bars a local agency from denying a permit for an unpermitted ADU or JADU built before January 1, 2020 unless the unit must be corrected to address a substandard condition under Health and Safety Code 17920.3, and it allows a confidential third-party inspection. Official source
• The City of Riverside Design Standards for Accessory Dwelling Units on Historic Properties were adopted February 19, 2025. The document says that as of January 2024 the City was receiving on average three to five ADU applications per month on historic properties, covering new structures, additions and conversions of existing structures, primarily garages, into ADU or JADU. It says the City was applying the Citywide Residential Historic District Design Guidelines adopted in 2003, and that owners may build an ADU under State law and Chapter 19.442 of the Riverside Municipal Code. Official source
• California Government Code Section 66317(a)(2)(A) requires a permitting agency to determine whether an accessory dwelling unit application is complete and give written notice of that determination to the applicant no later than 15 business days after receiving the application. Section 66317(a)(3) requires the permitting agency to approve or deny the application within 60 days from the date it receives a completed application, and states that if the local agency has not approved or denied the completed application within 60 days, the application shall be deemed approved. Official source
• California Government Code Section 66321(b)(3) states that no local lot coverage, floor area ratio, open space, front setback or minimum lot size rule may be applied that does not permit an accessory dwelling unit with at least 800 square feet of interior livable space and with four-foot side and rear yard setbacks to be constructed in compliance with all other local development standards. Section 66321(b)(4)(A) requires local agencies to allow a height of at least 16 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit. Official source
• California Government Code Section 66314(d)(5) states that the total floor area for a detached accessory dwelling unit shall not exceed 1,200 square feet. Section 66314(d)(10) limits parking to no more than one space per accessory dwelling unit or per bedroom, whichever is less, and Section 66314(d)(11) bars a local agency from requiring replacement parking spaces when a garage, carport or covered parking structure is converted to an accessory dwelling unit. Official source
• California Government Code Section 66311.5(c)(1) states that a local agency, special district or water corporation shall not impose any impact fee upon the development of an accessory dwelling unit that has 750 square feet of interior livable space or less, or a junior accessory dwelling unit that has 500 square feet of interior livable space or less. Any impact fees charged for an accessory dwelling unit that has more than 750 square feet of interior livable space are charged proportionately against the square footage of the primary dwelling. Official source