Garage Conversions: Antioch vs Brentwood
How do garage conversions rules compare between Antioch, CA and Brentwood, CA?
Antioch has fewer restrictions than Brentwood.
Antioch, CA
Contra Costa County
Antioch follows California state law allowing ministerial, by-right conversion of an existing garage into an ADU, with no setback added beyond fire-safety distance, no replacement parking required, and no fire-sprinkler requirement unless the primary dwelling already has sprinklers.
View full Antioch rules →Brentwood, CA
Contra Costa County
Brentwood garages must meet California Residential Code requirements for fire separation, including 5/8-inch Type X drywall on walls and ceilings separating the garage from living space and a self-closing, self-latching 20-minute fire-rated door. Conversion to an ADU is permitted by right under AB 68, and the city cannot require replacement parking for transit-adjacent conversions.
View full Brentwood rules →Key Facts Comparison
| Fact | Antioch | Brentwood |
|---|---|---|
| Code section | AMC § 9-5.3805 (Accessory Dwelling Units) | - |
| State law | Gov. Code § 65852.2 / §§ 66310-66342 | - |
| Approval | Ministerial, 60-day review | - |
| Setback for in-place conversion | None added beyond existing structure | - |
| Parking replacement | Not required when garage demolished/converted | - |
| Fire sprinklers | Not required if primary dwelling lacks them | - |
| Same-footprint rebuild | Allowed for ADU conversion | - |
| Pre-1/1/2020 legalization | AB 2533 path if H&S § 17920.3 met | - |
| - | - |
Highlighted rows indicate differences between cities.
Antioch FAQ
Can I turn my detached garage into an ADU in Antioch?
Yes. Antioch confirms conversion ADUs can be created from an attached garage, detached garage, accessory structure, or storage area. The City may also approve tearing down a detached garage or shed and rebuilding it in the same location to the same dimensions for the ADU.
Do I have to replace the parking I lose when I convert my garage?
No. California Government Code Section 65852.2 prohibits the City from requiring replacement of off-street parking spaces when a garage, carport, or covered parking structure is demolished or converted in conjunction with an ADU.
Do I need to add fire sprinklers to a converted-garage ADU?
Not if the primary residence does not already have fire sprinklers. State law prohibits a sprinkler requirement on an ADU when the existing single-family home is not sprinklered.
What if my garage was already converted without a permit?
Under AB 2533 you may apply to legalize an ADU constructed before January 1, 2020. The unit must be brought up to Health and Safety Code Section 17920.3 standards covering sanitary, structural, electrical, plumbing, mechanical, and weather-protection requirements before the permit can be issued.
Brentwood FAQ
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