Everything homeowners need to know about building an accessory dwelling unit in Riverside - size limits, setbacks, permits, and how Inland Empire lot sizes and construction costs compare to coastal Orange County.
Last verified: August 2026
9/10 · Very ADU-friendly
1,200 sq ft
Max ADU size
30 ft*
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes California's statewide ADU law and City of Riverside standards (Municipal Code Chapter 19.442) for general reference - it is not legal advice. Regulations change; always confirm current requirements with Riverside Building & Safety before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build or garage conversion)
1,200 sq ft, with at least an 850 sq ft ADU guaranteed regardless of other site constraints
Up to 30 ft in most zoning districts, typically allowing two stories
Height follows the zoning limit for the primary dwelling on your lot - confirm with Planning
1,200 sq ft or 50% of the primary dwelling's floor area, whichever is smaller
Up to 35 ft in most zoning districts, matching the height allowed for the primary dwelling
May be built above an existing garage or as a second-story addition, provided setbacks are met
Allowed zoning districts
Any residentially zoned lot with an existing or proposed primary dwelling, citywide. ADUs are allowed in side and rear yards only, not front yards. Riverside's larger, more typical Inland Empire lot sizes compared with coastal Orange County generally make it easier to fit a detached unit within the required setbacks.
Additional standards
Setbacks, parking & other rules
Setbacks
4 ft from side and rear property lines and from other buildings for the first floor; a second floor, if included, cannot be located within the side or rear setback at all; no additional setback for a conversion of an existing structure
Parking
Not required for an ADU or a JADU under any circumstance, including when a garage serving the primary home is converted
Units per lot
One ADU and one JADU per single-family lot
Owner-occupancy
Not required for a standard ADU; required for a JADU, with a recorded deed restriction naming the primary home or the JADU as owner-occupied
Building code
Must meet current California Residential Code standards; converting an existing structure may require upgrades to meet code
Unpermitted ADUs
A 2025 state law (AB 2533) gives the city a compliance process to legalize some existing unpermitted ADUs and JADUs rather than requiring their removal - worth asking about if you have an older, unpermitted unit on your property
Ordinance history
How Riverside's ADU rules got here
2017Statewide by-right ADU approval begins. California law requires cities to ministerially approve qualifying ADU applications, without discretionary review or a conditional use permit.
2020Eligibility confirmed citywide. Following a package of state bills (AB 68, AB 881, AB 587, AB 2299, AB 671) effective January 1, Riverside confirms that all residential properties are eligible for at least one ADU, and single-family lots for a JADU as well.
2022Local ordinance updated. The City Council adopts Ordinance No. 7592 on July 5, updating Municipal Code Chapter 19.442 covering ADUs.
2024Owner-occupancy eliminated; multifamily ADUs expanded. AB 976 permanently bars California cities from requiring owner-occupancy for standard ADUs; SB 1211 lets qualifying multifamily properties add up to eight detached ADUs.
2025Path to legalize unpermitted units. AB 2533 takes effect January 1, giving Riverside a process to bring existing unpermitted ADUs and JADUs into compliance rather than requiring removal.
Riverside doesn't require any parking for an ADU or JADU, in any circumstance, which is more permissive than many nearby cities. Larger, more typical Inland Empire lot sizes compared with coastal Orange County also tend to make it easier to fit a detached unit within the required setbacks without triggering more complex site-planning issues.
Permit process
How Riverside ADU permitting works
1
Pre-application check
Confirm your zoning and lot conditions with Planning (951-826-5800) before finalizing a design.
2
Choose your path
Riverside offers a pre-approved ADU plan program that's already been vetted for code compliance, which can meaningfully shorten your review compared with a fully custom design.
3
Prepare your plan set
Plans must be prepared by a licensed design professional and include a site plan, floor plans, and elevations.
4
Submit to Building & Safety
Ministerial ADU review is capped at 60 days from a complete application under state law; pre-approved plans commonly move in roughly 3-5 days, with custom designs closer to 10-20 days.
5
Building permit & inspections
Pull your building permit and schedule the standard framing, plumbing, electrical, and final inspections.
6
Utility connections
Decide whether the ADU will share utilities with the main house or get separate metered connections, and coordinate with Riverside Public Utilities and Public Works as needed.
Fees and timelines are approximate - contact Building & Safety (951-826-5697) for current figures.
Budgeting
What it costs to build an ADU in Riverside
Garage conversion
Roughly $70,000-$160,000, generally at the lower end of statewide ranges given Inland Empire labor and material costs
New detached ADU
Roughly $150,000-$300,000, also typically running below coastal Orange County pricing for a comparable unit
Attached addition / above-garage unit
Costs vary based on structural and utility work needed; get multiple contractor bids
Plan check & permit issuance fees
Vary by project valuation; contact Building & Safety (951-826-5697) for current figures
Development impact fees
Apply to some, not all, ADU projects depending on size and location; confirm what applies to your specific property
CalHFA ADU grant
Qualifying homeowners may be eligible for up to $25,000 in state pre-development cost assistance through CalHFA, subject to fund availability
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and whether utilities need to be extended.
Before you apply
Tips for a smooth approval
Ask about the pre-approved plan program first. A pre-vetted design can cut weeks off your review timeline compared with a fully custom plan.
Don't budget for parking you don't need. Riverside doesn't require any additional parking for an ADU or JADU, which is worth confirming early since some contractors default to including it.
Watch your setback on the second floor. The first floor of a detached ADU can sit within 4 ft of the property line, but any second floor must be built entirely outside that setback area, which affects your buildable footprint.
If you have an existing unpermitted unit, ask about legalization. A 2025 state law gives Riverside a path to bring some existing unpermitted ADUs and JADUs into compliance rather than requiring their removal.
Budget separately for utility connections. Whether the ADU shares utilities with the main house or gets its own connections affects both up-front cost and monthly billing.
FAQ
Common questions
Do I need to live on the property to build an ADU in Riverside?
No, not for a standard ADU. Owner-occupancy hasn't been required for ADUs statewide since a 2024 change in California law (AB 976). A junior ADU (JADU) still requires the owner to occupy either the primary home or the JADU.
How many ADUs can I build on one lot?
One ADU and one JADU on a single-family lot.
Do I need extra parking for an ADU?
No. Riverside doesn't require additional parking for an ADU or a JADU under any circumstance, even if a garage serving the primary home is converted.
How long does the permit process take?
State law caps ministerial review at 60 days from a complete application; using Riverside's pre-approved ADU plan program can bring that down to roughly 3-5 days in many cases.
What's the maximum size for a detached ADU?
Up to 1,200 sq ft, with height following the same limits as the primary dwelling, commonly up to 30 ft for detached units in most zoning districts.
How much does an ADU cost to build in Riverside?
Garage conversions tend to run roughly $70,000-$160,000, and new detached units commonly run $150,000-$300,000, generally at the lower end of statewide ranges given Inland Empire construction costs, based on local contractor estimates and regional reporting.
I have an old unpermitted ADU on my property. What are my options?
A 2025 state law (AB 2533) gives Riverside a process to bring some existing unpermitted ADUs and JADUs into compliance rather than requiring removal. Contact Building & Safety to ask about the city's compliance program.
Can I rent my ADU out on Airbnb or a short-term rental platform?
Confirm current short-term rental rules with the city before finalizing your design, since those rules are handled separately from ADU zoning.
