ADUs in San Diego County: the City of San Diego's rules and state law

Who sets the rules where you live

San Diego County has 18 cities and a large unincorporated area. Each writes its own ADU rules, and all of them start from state law (Government Code sections 66310 to 66342). A city may be more generous than state law, not stricter, and where the two conflict, state law wins.

In the City of San Diego, the rules are in San Diego Municipal Code section 141.0302, last amended by an ordinance that took effect July 15, 2026, and the Development Services Department issues the permits. ADUCheck gives full reports there, using the City's rules. For Carlsbad, Chula Vista, Oceanside, Escondido and the other cities, and for unincorporated communities such as Ramona, Alpine and Fallbrook, reports use the state rules and are labelled State rules only.

How many ADUs the City of San Diego allows

The City's page says ADUs are allowed in single-dwelling, multiple-dwelling, mixed-use and Planned District Ordinance zones. Junior ADUs are allowed only in single residential zones.

• Single-family property. One ADU inside the home or an existing accessory building, which may add up to 150 sq ft for an entry, plus one attached or detached ADU, plus one junior ADU.
• Proposed multifamily building. Up to 2 detached ADUs.
• Existing multifamily building. ADUs in non-livable space, at least one and up to 25 percent of the existing homes, plus up to 8 detached ADUs, not more than the number of existing homes.

There is no minimum property size, and ADUs do not count against the zone's density. Information Bulletin 400 says attached ADUs are not allowed in multifamily zones; state law may allow one, so check with the City for a multifamily property.

A property that used the City's urban lot split rules generally cannot add an ADU or junior ADU afterward. Check with the City before combining the two.

Size

• Attached or detached ADU. 150 sq ft to 1,200 sq ft.
• ADU inside the home or an existing accessory building. No maximum, plus up to 150 sq ft for entry in an accessory building.
• Junior ADU. 150 to 500 sq ft, inside the home or an attached garage, with an efficiency kitchen and its own exterior entry.

The City code has no rule tying an attached ADU to half the home's size. It measures size as gross floor area, while state law, since January 1, 2026, measures interior livable space, which leaves out wall thickness. State law controls, so a plan close to a limit should be checked with the City.

Height and setbacks

An ADU follows the height limit of its base zone and any overlay zone, with no separate 16 ft cap. On a property with only single-family homes, a detached ADU can be no more than two stories. Near the coast, check with the City on the height overlay.

• Front. The base zone's front setback, except that one attached or detached ADU of 800 sq ft or less, if it is the only one on the property, is exempt from the front setback, lot coverage, floor area ratio and open space limits.
• Street side. 4 ft, or the zone's street side setback if less.
• Side and back, outside fire zones. An ADU 16 ft tall or less needs no setback, unless the Fire Code Official requires one. An ADU over 16 ft keeps 4 ft where that side or back faces a residential neighbor.
• Side and back, in a High or Very High Fire Hazard Severity Zone. At least 4 ft at any height. The City's page names only the Very High zone; the code says High or Very High.
• Decks, balconies and outside stairs. These meet the base zone setbacks.
• Conversions. A converted or same-footprint rebuilt structure keeps its existing setbacks.

The City's bulletin adds that building code fire separation rules can mean a larger setback, and a site in a brush management zone may need more.

Parking

No parking is required for ADUs or junior ADUs, with one exception. In the Beach Impact Area of the Parking Impact Overlay Zone, outside a transit priority area, each ADU needs one off-street space unless it is 500 sq ft or less, in a historic district, attached to the home or an accessory building, in a residential permit parking district, or within one block of a car share vehicle. A garage or carport converted or torn down for an ADU is replaced only in that same area. If the project leaves the driveway under 18 ft long, the City requires the curb cut to be closed.

The Coastal Overlay Zone

Inside the Coastal Overlay Zone, an older version of the ADU code applies until the Coastal Commission certifies the newer amendments. A coastal development permit is generally required for an ADU or junior ADU that is not entirely inside the existing home, adds habitable area or converts non-habitable space. The City issues it, and since September 2022 the City's ADU coastal permit decision is not appealable to the Coastal Commission. For any coastal address, check with Development Services before you design.

Fees in the City of San Diego

• Development impact fees. Exempt for ADUs under 750 sq ft and for all junior ADUs. The first two ADUs on a property are exempt at any size, with an exception for lot split projects over 750 sq ft.
• General Plan Maintenance Fee. $737, once per project, according to Information Bulletin 501 (August 2026).
• Plan check and inspection. For an attached ADU or junior ADU up to 1,100 sq ft, or a detached ADU up to 500 sq ft, Information Bulletin 501 lists plan check at about $3,512.92 for the first 500 sq ft plus $6.98 per sq ft, and inspection at about $2,228.29 plus $4.46 per sq ft. Larger projects use a different table.
• School fees. A new detached ADU or junior ADU of less than 500 sq ft is exempt. Above that, the school district sets the rate.
• Water and sewer capacity. Charged in plan review. Check the current amount with the City's Public Utilities Department.

Owner occupancy and renting

No owner has to live on the property because of an ADU. For a junior ADU, the owner must live in the home or the junior ADU only if it shares a bathroom; the City's bulletin and state law agree, though the code text is older. The City still requires a recorded junior ADU agreement before the permit. ADUs and junior ADUs are rented for more than 30 days, and a junior ADU cannot be sold separately from the home.

Pre-approved plans and review time

The City does not publish its own plans. It accepts pre-approved plans from the County of San Diego, Chula Vista and Encinitas, with a 30-day review. You license the plan from its provider, and it must meet the codes in force when you submit. ADU permits are a ministerial staff decision. For other applications, state law gives 15 business days to confirm the application is complete and 60 days from a complete application to decide.

The bonus ADU program

The City's ADU Home Density Bonus allows extra ADUs in exchange for deed-restricted affordable ADUs, with an agreement with the San Diego Housing Commission. It depends on the zone, fire zone, maps of resource areas and the size of the property. A property may qualify; it takes a review to know.

The other cities and unincorporated San Diego County

Outside the City of San Diego, start from the state rules. A detached ADU can be up to 1,200 sq ft, and every city must allow at least 800 sq ft at 16 ft tall with 4 ft from the side and back of the property. Height is 16 ft, or 18 ft near major transit plus 2 ft to match the roof pitch. No parking can be required within half a mile walking of transit, for a conversion, or in the other cases state law lists. No impact fees apply up to 750 sq ft. The city must decide within 60 days of a complete application.

Unincorporated areas are handled by the County's Planning & Development Services. In July 2026 HCD found the County's ordinance out of compliance with state law on several points, including how size is measured and which ADUs can be combined. Where they conflict, state law applies, so check with the County on any number in its code.

A guide is a starting point, not a permit. Enter your address at aducheck.com and the report shows what fits on your property, with the source and date for each fact.