California ADU rules · Contra Costa County
Can I Build an ADU in Antioch?
Yes — you can build an ADU in Antioch. California's statewide ADU law requires every city, including Antioch, 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, detached, or conversion) + 1 JADU (conversion only) + 1 detached new-construction ADU up to 800 sqft if all standards are met
Allows an additional detached ADU up to 800 sqft beyond the standard 1 ADU + 1 JADU.
Units on a multifamily lot
Local ruleConversions (up to 25% of units, minimum 1) + up to 2 detached new-construction ADUs per lot
Detached new-construction ADUs on multifamily lots capped at 2 per lot.
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
Local rule1,000 sq ft
Detached ADUs: 850 sqft (studio/1-bed), 1,000 sqft (2-bed); state floor of 800 sqft always allowed.
Max attached ADU size
Local rule850 (studio/1-bed), 1,000 (2-bed), and no more than 50% of primary dwelling; must allow at least 800 sqft
Both numeric and percentage caps apply, but 800 sqft must always be allowed.
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 rule30 ft from front property line; 20 ft from street-facing property line if different; conversions exempt
Front setback is more restrictive than state default; conversions exempt.
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleUp to 1 space
1 off-street space per ADU unless exempt; exemptions mirror state law.
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 parking lost to ADU 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 after Jan 1, 2020; JADUs require owner-occupancy.
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
Local ruleBuilding permit, ADU permit (for new detached ADUs >800 sqft or new attached ADUs)
ADU permit required for certain new construction ADUs in addition to building permit.
Antioch-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Sprinkler requirements
Sprinklers required in ADU only if required in primary dwelling.
Historic district garage conversion
No special demolition notice required for garage conversion unless in historic district.
Antioch limits detached and attached ADUs to 850/1,000 sqft (studio/1-bed/2-bed), with a unique allowance for an extra detached ADU up to 800 sqft on single-family lots. Front setbacks are more restrictive than state minimums, and multifamily lots are capped at 2 detached ADUs.
Frequently asked questions
Can I build an ADU in Antioch?
Yes. California's statewide ADU law requires Antioch 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 Antioch?
A detached ADU of at least 1,000 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 Antioch?
Side and rear setbacks are limited to 4 ft. 30 ft from front property line; 20 ft from street-facing property line if different; conversions exempt.
Is parking required for an ADU in Antioch?
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 Antioch?
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 Antioch?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Antioch Municipal Code § 9-5.3805 (ADUs & JADUs), Ord. 2243-C-S (Dec. 10, 2024)
- § 9-5.3805(D)(1)(a)-(b)
- § 9-5.3805(D)(1)(c)-(d)
- § 9-5.3805(F)(1)(a)-(c)
- § 9-5.3805(F)(1)(b)-(c)
- § 9-5.3805(F)(3)
- § 9-5.3805(F)(5)
- § 9-5.3805(F)(5)(c)
- § 9-5.3805(E)(6)
- § 9-5.3805(D)(2), (H)(1)
- § 9-5.3805(E)(3)
- § 9-5.3805(F)(5)(b)
- 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)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-25. This is an AI-assisted summary of Antioch'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 Antioch Planning before relying on it.
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