California ADU rules · Solano County
Can I Build an ADU in Rio Vista?
Yes — you can build an ADU in Rio Vista. California's statewide ADU law requires every city, including Rio Vista, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
Local rule1 ADU (attached or detached) + 1 JADU per parcel
Units on a multifamily lot
Local ruleup to 2 detached ADUs per parcel + conversions within existing building up to 25% of units
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
CA state law1,200 sq ft
Statewide default cap for detached new-construction ADUs in the absence of a compliant local ADU ordinance. The unconditional by-right floor a city must always allow is 800 sq ft (see Guaranteed minimum size); a city with a compliant ordinance may set its own ceiling.
Max attached ADU size
Local rule1,200 sq ft or 50% of primary dwelling, unless needed to reach 800 sq ft
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
CA state law16 ft
16 ft baseline; cities must allow 18 ft within ½ mi of a major transit stop or where the primary dwelling is two-story, and 20 ft on a lot with a multistory multifamily building.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
Local rulePer zoning district for primary dwelling; ADUs not allowed between primary dwelling and front lot line
Separation from main house
Local ruleNone required
No specific minimum; must comply with underlying zone/building code.
Parking
Parking required
Local ruleUp to 1 space
1 per ADU unless exempt; no parking required for JADUs.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement required for garage/carport/covered parking conversion.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
No owner-occupancy for ADUs permitted 2020-2024; required for ADUs permitted on/after Jan 1, 2025. JADUs always require owner-occupancy.
Impact-fee waiver
Local ruleWaived under 750 sq ft
No impact fees for ADUs <750 sq ft or for JADUs.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Rio Vista allows up to 2 detached ADUs on multifamily lots and limits detached ADU height to 16 ft (18 ft for multifamily/multistory lots). Owner-occupancy for ADUs is waived until 2025, after which it is required.
Frequently asked questions
Can I build an ADU in Rio Vista?
Yes. California's statewide ADU law requires Rio Vista to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Rio Vista?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Rio Vista?
Side and rear setbacks are limited to 4 ft. Per zoning district for primary dwelling; ADUs not allowed between primary dwelling and front lot line.
Is parking required for an ADU in Rio Vista?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Rio Vista?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Rio Vista?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Rio Vista Municipal Code § 17.44.030 (Ord. 001-2024, 2/20/2024)
- § 17.44.030(E)(1)(a)-(b)
- § 17.44.030(E)(1)(c)-(e)
- § 17.44.030(E)(6)(d)
- § 17.44.030(E)(5)(a)
- § 17.44.030(E)(5)(a)(iv)
- § 17.44.030(E)(8)(a), (d)
- § 17.44.030(E)(8)(c)
- § 17.44.030(F)
- § 17.44.030(G)(1)-(2)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
Last updated 2026-06-25. This is an AI-assisted summary of Rio Vista's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Rio Vista Planning before relying on it.
Will an ADU work on your Rio Vista lot?
Ask GoCodebook about your address and get the size, setback, parking and permit rules that actually apply to your parcel — with the exact citation.
Check my parcel free