California ADU rules · Solano County
Can I Build an ADU in Vallejo?
Yes — you can build an ADU in Vallejo. California's statewide ADU law requires every city, including Vallejo, 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
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
CA state lawConversion ADUs (≥1, up to 25% of units) + up to 8 detached
Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.
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 rule50% of the primary dwelling's living area, or 1,200 sq ft, whichever is less; the state minimums (≥850 sq ft, ≥1,000 sq ft for 2+ bedrooms) must still be allowed
Vallejo's 2018 ordinance frames the attached-ADU cap as the lesser of 50% of the primary or 1,200 sq ft. State law guarantees ≥850 sq ft (≥1,000 for 2+ bedrooms) regardless, so the '50%' figure cannot drop an ADU below those floors.
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
CA state lawNo front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
CA state lawUp to 1 space
At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.
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
CA state lawNot required
When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.
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
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Vallejo-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
2018 ordinance predates current State ADU Law
Vallejo's Ch. 16.303 dates to 2018 and, per HCD's 2025-10-08 Letter of Technical Assistance, has not been updated for the many intervening ADU-law changes. Provisions in the 2018 text that conflict with state law — notably a recorded deed restriction, a short-term-rental prohibition tied to that deed restriction, and any owner-occupancy condition on an ADU — are preempted and unenforceable today. State law governs where the local text conflicts.
Coastal / waterfront areas
ADUs on parcels within a local coastal program area must comply with both state ADU law and applicable coastal-resource policies; a coastal development permit or exemption may be required.
Hillside development standards
Vallejo's hillside grading and building standards may apply on sloped lots, but cannot preclude at least one state-mandated 800 sq ft ADU.
Vallejo has a local ADU ordinance — Vallejo Mun. Code Ch. 16.303, adopted July 10, 2018 — but it is materially OUT OF DATE. HCD's October 2025 Letter of Technical Assistance to the City catalogs the ADU-law changes since 2018 (the 2024 SB 477 recodification to Gov. Code §§ 66310 et seq., the bar on deed restrictions and owner-occupancy mandates for ADUs, the no-parking rule for JADUs, eight detached ADUs on multifamily lots, the 60-day deemed-approved rule) that the 2018 ordinance never absorbed. Practically: detached ADUs up to 1,200 sq ft, 16-ft height, 4-ft side/rear setbacks, and the standard transit/conversion parking exemptions apply — but treat the 2018 deed-restriction, short-term-rental, and owner-occupancy language as preempted, and confirm the current rules with Vallejo Planning before relying on the code as written.
Frequently asked questions
Can I build an ADU in Vallejo?
Yes. California's statewide ADU law requires Vallejo 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 Vallejo?
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 Vallejo?
Side and rear setbacks are limited to 4 ft. No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone.
Is parking required for an ADU in Vallejo?
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 Vallejo?
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 Vallejo?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Vallejo Mun. Code Ch. 16.303 (Accessory Dwelling Units)
- Vallejo Mun. Code Ch. 16.303
- HCD Letter of Technical Assistance to City of Vallejo (2025-10-08)
- 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 § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66314 (local ordinance standards)
- Cal. Gov. Code § 66315 (owner-occupancy)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-28. This is an AI-assisted summary of Vallejo'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 Vallejo Planning before relying on it.
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