Antioch Zoning and ADU Guide for Homeowners

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Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team.

An Antioch single-family lot can host up to three added units: one junior ADU, one conversion ADU and one small detached ADU of 800 square feet or less. This guide summarizes the city’s published ADU handout for homeowners, including size, height, setbacks, parking, owner occupancy, rental rules and fees, and explains what an ADU or unpermitted garage conversion means when you sell.

Antioch ADUs at a glance

Office	Planning Division and Building Services Division, City of Antioch
Building Services phone	(925) 779-7065
Single-family lot	Up to one JADU, one conversion ADU and one small detached ADU (800 sq ft or smaller), for up to three added units
Larger ADU	One large detached or attached ADU under an ADU permit
Multifamily	Conversion ADUs: at least one and up to 25 percent of existing units; detached: up to eight
Short-term rentals	Prohibited
Pre-approved plans	The city has a Pre-Approved ADU Plan Program for designers

Antioch ADU standards

Junior ADU size	500 sq ft or less
Small detached or attached ADU	800 sq ft or smaller
Large detached or attached ADU	850 sq ft for studio and one bedroom, 1,000 sq ft maximum; if attached, no more than 50 percent of the primary dwelling’s floor area
Height	16 feet generally; 18 feet for a detached ADU within a half mile of a major transit stop, with up to two more feet to match the main roof pitch; attached ADUs up to 25 feet, no more than two stories
Side and rear setbacks	4 feet (conversions need only enough for fire safety)
Front setback for a large ADU permit	30 feet front; 20 feet on another street-facing line
Distance from the main home	5 feet for a detached ADU

Parking

The handout lists no parking requirement for junior ADUs, conversion ADUs and small ADUs, and generally one space for a large ADU under the ADU permit.

A parking space is not required if the ADU is within one-half mile walking distance of public transit, in an architecturally and historically significant historic district, in an area where on-street permits are required but not offered to the occupant, or within one block of a car-share stop.

An unenclosed space is at least 8.5 by 18 feet, and a garage space at least 10 by 20 feet with 7.5 feet of vertical clearance.

Owner occupancy, rentals and fees

Owner occupancy of one unit is required for junior ADUs.
Short-term rentals are prohibited.
Impact fees do not apply to junior ADUs or to conversions under 750 square feet. For ADUs of 750 square feet or more, fees must be proportional to the square footage of the existing dwelling.
Plan check fees are issued by the Building Division, and other agencies may collect fees before the permit is issued.

Utilities and outside agencies

The handout lists the agencies a project may touch: the Antioch Unified School District for school fees, Delta Diablo for sanitation, the Contra Costa Fire Protection District, Contra Costa County Environmental Health, PG&E, and Republic Services. Contact them early, because service letters and fees can affect your schedule.

How the Antioch process works

Check which ADU types fit. Decide among a junior ADU, a conversion, a small detached unit or a larger unit.
Consider pre-approved plans. The city’s program lets designers submit ADU plans to be pre-approved, which may shorten design time.
Review submittal requirements. The city’s How to Apply page lists the ADU requirements, and a meeting with a city planner is optional but highly recommended.
Apply through the Online Permitting System. Building permits for ADUs go through the same portal as other permits.
Pay fees and inspect. Fees are due to several agencies, and inspections are scheduled online.

Legalizing an unpermitted ADU

The city says owners of an unpermitted or informal ADU should call Building Services at (925) 779-7065 to discuss retroactively receiving a permit. It adds that legalizing can bring peace of mind that you will not face code enforcement or tenant actions, along with higher property values, insurance coverage and increased safety. That is a useful starting point if you inherited a home with an old backyard unit or converted garage.

ADUs, garage conversions and selling an Antioch house

Many older homes have a converted garage or backyard unit built without permits. Buyers and lenders ask about them, and California sellers generally disclose known unpermitted work. Our guide to selling as-is with unpermitted work explains the rules, and our Prop 13 guide explains how new construction can affect property tax. A short checklist:

Check city records for permits on any ADU, conversion or addition.
Ask Planning whether the structure could qualify under current rules.
Estimate plans, fees and corrections needed to legalize it.
Compare that with selling as-is and letting a cash buyer take on the legalization.

Questions to ask Planning before you design

Which ADU type fits my lot, and does a pre-approved plan work?
What are the current impact and school fees for the size I am considering?
Do sanitation, fire and utility providers need to issue approvals first?
Can my existing garage be converted without changing its footprint?

Why ADUs matter for resale

A permitted ADU can add rental income and appeal for some buyers, but an unpermitted one can complicate financing and appraisal. Lenders typically want permitted living area, and an appraiser may not count unpermitted space. If you are not planning to stay, selling the house as it stands to a cash buyer lets the next owner decide whether to legalize.

How to sell a house in Antioch

Check which structures on the property are permitted ADUs, conversions or unpermitted.
Collect permits, plans and any city notices.
Request a no-obligation cash offer for the house as it stands.
Choose your closing date.
Close with no legalization, repairs or showings required.

Our local pages cover related situations in Antioch, including selling as-is, selling fast, selling during a divorce and relocating. See also our Antioch page and the Contra Costa County hub.

Own an Antioch home with an ADU or garage conversion? Sell as-is for cash.

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Frequently asked questions

How many ADUs can I build on an Antioch single-family lot?

The city’s handout says a property could include one JADU, one conversion ADU and one small detached ADU of 800 square feet or smaller, for up to three additional units.

How big can an Antioch ADU be?

Junior ADUs are 500 square feet or less. Small ADUs are 800 square feet or smaller. A large ADU is 850 square feet for a studio or one bedroom, and 1,000 square feet at most.

Does an ADU need parking in Antioch?

Generally one space for a large ADU permit, with exceptions such as being within a half mile of transit. Junior, conversion and small ADUs list no parking requirement.

Are short-term rentals allowed in an Antioch ADU?

No. The handout says short-term rentals are prohibited.

Do I have to live on the property?

Owner occupancy of one unit is required for junior ADUs.

Can I legalize an unpermitted ADU in Antioch?

The city invites owners to call Building Services at (925) 779-7065 to discuss retroactively receiving a permit.

Can I sell my Antioch house with an unpermitted ADU or garage conversion?

Yes. You can disclose it and sell as-is, including to a cash buyer. Our statewide guide explains the disclosure rules.

More guides

Sources

This guide is general information from public sources, not legal advice. Confirm current rules, fees and hours with the city.