Converting a garage into an ADU is one of the most efficient ways to add a legal home to a Bay Area lot. The walls, roof and slab already exist, and state law removes several barriers that used to stop these projects. A garage conversion still has to meet the building code for a dwelling, though, and that is where most of the work is.
What state law allows
- No replacement parking: when a garage is converted to an ADU, cities cannot require you to replace the lost parking spaces.
- Existing setbacks are fine: an ADU built within an existing structure, or rebuilt in the same footprint and dimensions, does not have to meet current setbacks.
- Small expansion: a conversion inside an existing structure can expand by up to 150 sq ft to accommodate entry and exit.
- No owner occupancy: cities cannot require the owner to live on site for an ADU.
- Unpermitted conversions: state law limits when a city can deny a permit to legalize an ADU built before 2020, unless it poses a health or safety risk.
Building code items to plan for
- Slab and moisture: garage slabs often slope toward the door and lack a vapor barrier. We level the floor and add moisture protection.
- Ceiling height: habitable rooms generally need at least 7 feet of ceiling height.
- Windows and egress: bedrooms need an emergency escape window of code size, and the garage door opening is usually replaced with a wall, window or door.
- Fire separation: if the garage is attached to the house, the shared wall and ceiling need fire-rated construction.
- Energy code: walls, ceiling and floor need insulation to meet California’s Title 24 energy standards, and new heating and water heating are often all-electric.
- Utilities: new plumbing for a kitchen and bathroom, sewer connection, and often an electrical panel upgrade.
The permit process
You submit plans for an ADU permit. Once the application is complete, the city has 60 days to approve or deny it. Expect a plan check round or two. San Jose and other cities have specific garage conversion guidance, which we cover on our San Jose garage conversion page.
Garage conversion or junior ADU?
If the garage is attached and you want a smaller unit that shares the main house, a junior ADU of up to 500 sq ft is another option. Junior ADUs require the owner to live in either the house or the junior unit.
Frequently asked questions
Can I convert my garage without adding parking?
Yes. California law does not allow cities to require replacement parking for a garage converted to an ADU.
How long does a garage conversion take?
Construction is often shorter than a new detached ADU because the shell exists, but the slab, utilities and energy upgrades still take time. Permits add a few months.
Learn more on our garage conversion ADU page.
Talk to a Licensed Bay Area Builder
Tell us about your lot and what you want to build. We will check your city’s rules and schedule a free consultation.
