Garage conversion ADU in San Diego: permits, cost and rules

Can I convert my garage into an ADU?

Almost always. State law requires every city to approve, on a single-family lot, one ADU built inside the existing space of the house or an existing accessory building, which includes a detached or attached garage. You can add a new detached ADU and a junior ADU on the same lot. In the City of San Diego, a garage conversion counts as that converted ADU.

Conversions get the friendliest rules in the law:

• No setbacks. A city can't require setbacks for an existing structure converted to an ADU, or for one rebuilt in the same place and to the same size, as long as it's sufficient for fire and safety.
• No size cap on existing space. A conversion isn't limited by the usual ADU size rules, and a detached garage can grow by up to 150 square feet for an entrance. San Diego's code sets no maximum size for conversions.
• Its own door. A conversion ADU needs exterior access separate from the main entrance of the house.
• No new utility hookup. A city can't require a new or separate utility connection, or charge a connection fee, for an ADU converted from existing space (unless it's built with a new house).
• No impact fees in San Diego. The city exempts the first two ADUs on a property from development impact fees, whatever their size.

For the full rule set, see our guide to California ADU laws, or start with what an ADU is.

Do I need to replace parking?

No. When a garage, carport or covered parking structure is converted to an ADU, or torn down to build one, a city can't make you replace those spaces. Separately, no parking can be required at all for an ADU that's part of an existing structure.

San Diego's code requires ADU parking only in the Beach Impact Area outside transit priority areas, and the city's bulletinflags exceptions in parts of the Coastal Overlay Zone. One practical catch: if your driveway no longer leads to a legal parking space after the conversion, the city can require you to close the curb cut. Ask about it at plan review, because closing a driveway adds concrete and curb work to the bid.

What a garage needs to become a home

The zoning rules are easy. The building code is where conversions get expensive, because a garage was built to park cars, not to live in. Here's what reviewers and inspectors look for.

Foundation and slab moisture

Many garage slabs were poured without a vapor barrier. Building departments typically require one under the new living space, either by replacing the slab or by using an approved membrane over the existing one. Los Angeles County's standard conversion details, for example, also require the existing slab to meet minimum thickness and be reasonably free of settlement cracks. Snap ADU notes older slabs and footings often fall short and may need retrofit footings or full replacement, and that plumbing requires saw-cutting the slab.

Insulation and the Title 24 energy code

The California Energy Commission treats a garage conversion as an addition, because unconditioned space becomes conditioned. It must meet the addition rules in Section 150.2(a) of the 2025 Energy Code. In practice that means insulated walls and ceiling, compliant windows, and an energy report (Title 24 calculations) with your plans.

Ceiling height

California's residential code requires habitable rooms to have a ceiling height of at least 7 feet. Most garages clear that, but a new raised floor over the slab, or a low beam, can push you under. Measure before you design.

Windows and emergency escape

Every sleeping room needs an emergency escape opening. Under the 2025 code it must have at least 5.7 square feet of net clear opening (5 square feet at grade floor), be at least 24 inches high and 20 inches wide, and sit no more than 44 inches above the floor. The big garage door opening usually becomes a wall with windows and an entry door.

Fire separation and sprinklers

If the garage is attached to the house, the wall and ceiling between the two homes need a 1-hour fire-resistance rating, or half an hour if the building is fully sprinklered. San Diego doesn't require sprinklers when converting existing permitted space into an attached ADU, since there's no change of occupancy or larger fire area. An ADU never needs sprinklers if the main house isn't required to have them.

Plumbing, sewer and electrical

A conversion needs a full kitchen and bathroom, which means new drain lines tied into the house sewer, and usually rerun wiring. The electrical service may need an upgrade. You can share the house's water and power, since the city can't require a separate connection for a conversion.

Garage conversion permit in San Diego

Converting a garage to living space always needs a building permit, even if the outside barely changes. In the City of San Diego, an ADU is a ministerial building permit with no public hearing, submitted online. State law gives the city 15 business days to confirm your application is complete and 60 days to approve or deny it, or it's deemed approved.

Building permit for garage conversion: what to submit

• A site plan showing lot status, parking and setbacks, prepared under the city's site plan bulletin.
• Floor plans, elevations and structural details for the converted garage.
• Title 24 energy calculations.
• Historical information if the structure is more than 45 years old.

Snap ADU notes that converting an attached garage also triggers a demolition permit, since the work alters the main house.

Garage ADU plans

The free and pre-approved ADU plans that get a 30-day review are for detached ADUs. A conversion is drawn around your existing garage, so plan on a designer measuring the building and preparing a custom set. See pre-approved ADU plans in San Diego if you're weighing a new build instead, and our step-by-step ADU permit guide for San Diego.

Garage conversion ADU cost

So how much does a garage conversion cost in San Diego? Builders' published ranges put it well below a new detached unit, because the walls, roof and slab already exist. The spread depends on the garage's condition: Snap ADU notes the cost of a conversion varies largely with the garage's condition and location.

City permit fees are a separate line. Snap ADU's February 2026 table puts City of San Diego fees at about $10,734 for a 499 sq ft ADU and $25,138 for 749 sq ft. Those are a builder's figures, not an official fee schedule. For the whole picture, see what an ADU costs in San Diego or try the ADU cost calculator.

Convert or tear down and rebuild

Keeping the old garage isn't always cheaper. Snap ADU says garages 30 or more years old are usually poor candidates, because bringing old framing, slabs and footings to code costs more than starting over, and that demolition adds only about a week to construction.

If you rebuild larger or taller than the old garage, the new part must meet normal ADU rules, including setbacks. Once the ADU permit is issued, a city can't withhold the permit to demolish the garage it replaces. For a taller option, see two-story ADUs.

Attached garage: ADU or junior ADU

An attached garage can also become a junior ADU: up to 500 square feet inside the house, with at least an efficiency kitchen, and it may share a bathroom with the house. State law counts an attached garage as part of the house for this.

• Size: a JADU tops out at 500 sq ft; a conversion ADU has no cap on existing space.
• Parking: state law lets a city require replacement parking when a JADU takes over an attached garage, unlike a full ADU. Confirm with the city before you design.
• Owner occupancy: San Diego's code requires the owner to live on site with a JADU.

Read more in our junior ADU guide and attached vs. detached ADUs.

Unpermitted garage conversions

Bought a house with a garage someone already turned into a unit without permits? If it was built before January 1, 2020, the citycan't deny a permit to legalize it just because it breaks building or zoning rules, unless a fix is needed for health and safety. It also can't charge impact fees for it.

Units are judged against the state's substandard-housing standard, and you may get a confidential inspection from a licensed contractor before you apply. San Diego lays out its process in Information Bulletin 242. A conversion done after 2020 goes through the normal permit process.

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Common questions