Guide
Can I build an ADU on my lot in San Diego?
The short answer
Usually, yes. State law lets most residential lots with a house, or a planned one, add an ADU, and the City of San Diego requires a building permit for every ADU or junior ADU. What your lot can hold depends on who reviews it (the City of San Diego, one of the 17 other cities, or the County), its zone and setbacks, its utilities, and whether it sits in a coastal or fire hazard area.
First, find out who reviews your lot
San Diego County has 19 permit authorities: the City of San Diego, 17 other incorporated cities, and the County for the unincorporated areas. State ADU law applies in all of them, and each can add local rules within its limits, so the first question is not "can I" but "who decides".
In the City of San Diego a building permit is required to create an ADU or a junior ADU, with no exemptions. In the unincorporated County you also need a building permit, and the property must be residential with an existing or planned house on it.
What the City of San Diego allows on a single-family lot
On a lot in a single-dwelling zone the City permits the house plus one ADU attached to or detached from it, one more ADU converted from existing space or an existing accessory structure, and one junior ADU. ADUs are generally allowed wherever the zone allows homes.
| Rule | What applies in the City of San Diego |
|---|---|
| Size | 150 to 1,200 square feet of gross floor area for an attached or detached ADU. A conversion of existing space is not subject to the 1,200-square-foot cap. |
| Junior ADU | 150 to 500 square feet inside the house or its attached garage, with its own exterior entrance and a kitchen or efficiency kitchen. |
| Height | The height limit of the zone. On a single-dwelling lot a detached ADU may be two stories. |
| Setbacks | The front setback of the zone. At the sides and rear, 4 feet or the zone's setback, whichever is less, when the ADU is over 16 feet tall next to a residential lot. In a Very High Fire Hazard Severity Zone a new ADU stays at least 4 feet from the side and rear lines at any height. |
| Parking | None in most of the City. In the Beach Impact Area outside a transit priority area, each new ADU needs one space unless it is 500 square feet or less, attached, in a designated historical district or a residential permit parking district, or within a block of a car share vehicle. A garage, carport or covered space converted or torn down there must be replaced. Each bonus ADU outside a transit priority area needs one space. |
| Owner occupancy | Not required for an ADU. For a junior ADU, only when it shares a bathroom with the house, and then you live in the house or the junior ADU. |
| Rentals | 31 consecutive days or longer for an ADU or a junior ADU, so neither can be a short-term vacation rental. |
| Fire sprinklers | Only when the main house has them. Building a detached ADU does not force sprinklers into the house. |
| Solar | Required on a newly built detached ADU under the state Energy Code, on the ADU or the house. Not required on a conversion or a JADU. |
The code's fire rules say High or Very High Fire Hazard Severity Zone, but the City's adopted fire map shows only Very High zones, so look your lot up on that map. In those zones the bonus program also has street and access rules of its own, covered in the bonus program guide. The 4-foot fire setback came with the 2025 amendments, which don't reach the Coastal Overlay Zone until the Coastal Commission certifies them, so on a coastal lot ask the City which setback it will apply.
Some of the City's own documents haven't caught up with these rules:
- The City's ADU page mentions parking in the Beach Impact Area only for garage conversions. The code requires a space for a new ADU there too. A 650 square foot detached ADU there, with no car share nearby, needs one space; a 480 square foot one needs none. Confirm at intake whether your lot is in the Beach Impact Area and a transit priority area.
- The Municipal Code and its junior unit agreement still say the owner must live on the lot with every junior ADU. State law has limited that to a shared bathroom since January 1, 2026, and the City's bulletin follows it. Ask the City at intake which version of the agreement it will record for you.
- The code text still says a junior ADU has no rental limit. State law has required more than 30 days since January 1, 2026, and the City's bulletin follows it.
An ADU counts toward the lot's floor area ratio, but the City allows one ADU of up to 800 square feet even when the lot is already at its limit, and one ADU of 800 square feet or less may sit inside the front setback.
More ADUs are possible on qualifying lots through the City's ADU Home Density Bonus Program, capped by lot size at four, five or six ADUs and JADUs in total. The 2025 amendments to that program took effect on August 22, 2025 outside the Coastal Zone and apply inside it only once the Coastal Commission certifies them, which the City expects in 2026.
What state law guarantees everywhere in the county
Every city and the County must follow the state's ADU law, as HCD's handbook sets it out. Whatever the local ordinance says, these hold:
- A permitting agency must approve or deny a complete ADU application within 60 days when a house already stands on the lot, and must tell you within 15 business days whether your application is complete.
- A lot with a house must be allowed at least one detached ADU of up to 800 square feet with 4-foot side and rear setbacks. From January 1, 2027, under AB 956, a single-family lot gets two of them, newly built, and once both are built the permit office need not also approve a junior ADU.
- A homeowners association cannot prohibit or unreasonably restrict an ADU or JADU on a lot zoned for single-family homes, and from January 1, 2027 on any lot zoned to allow a house. Such rules are void.
- Owner occupancy cannot be required for an ADU. For a JADU it is required only when the JADU shares a bathroom with the house.
- Fire sprinklers cannot be required in an ADU or a JADU when the main house does not have them.
Fees
State law exempts an ADU with 750 square feet of interior livable space or less, and a JADU with 500 square feet or less, from impact fees. Above that, an ADU's impact fee is charged in proportion to the main house; from January 1, 2027, on a lot with one or two ADUs, SB 1117 limits that charge to the area above 750 square feet. School districts may charge fees only above 500 square feet of assessable space, and an ADU under 500 square feet does not add to it.
The City of San Diego lists its construction permit fees in Information Bulletin 501. Its Municipal Code exempts every junior ADU and any ADU under 750 square feet of gross floor area from the City's development impact fees, and the first two ADUs on a lot at any size, unless they are built under the City's SB 9 rules. School fees and the General Plan Maintenance Fee still apply as the City's ADU bulletin describes. The County's trial impact fee waiver ended on January 9, 2024.
Utilities and the site itself
- Power. SDG&E asks you to get an address for the ADU from the city or the County before you apply, then to apply through My Project Center and allow two weeks for its review.
- The driveway. In the City, if an ADU or a garage conversion leaves an existing driveway shorter than City standards, the driveway has to be closed.
- Fire separation. ADUs must meet the California Building Standards Code, including fire separation distance from other buildings, which can push an ADU further from the house or the property line than the zoning setback alone.
- Slope, access and utility runs move the cost, and the cost calculator prices each of them. In a fire hazard zone, street access can also decide whether bonus ADUs are allowed at all.
How long it takes
The City's permit timeline page gives a weekly snapshot of its intake, review and issuance queues (its latest data is dated October 9, 2026) and asks for complete submittals, because every recheck adds a cycle. An application that uses one of the preapproved plans the City accepts gets a 30-day review.
For the whole path, a third-party analysis of the City's permit records put the average completed detached ADU at about 24 months from submission to final inspection, with 43% of the detached ADUs submitted at least three years earlier reaching final inspection within three years. Treat that as one firm's reading of public data, not a promise.
What changes the answer
The rules table above is the City of San Diego's. These are the cases where the answer moves.
Another city
Each of the 17 other cities sets its own ADU rules within state law. Find your authority first, then read its page.
The unincorporated County
The County caps an attached ADU at half the house's floor area, up to 1,200 square feet, and a detached ADU at 1,200 square feet regardless of the house. It offers its own standard plans, and on March 4, 2026 it adopted a program for selling an ADU separately through condominium conversion.
The Coastal Overlay Zone
In the City's Coastal Overlay Zone a Coastal Development Permit is required for most ADUs, and several of the City's newer ADU rules are not yet in effect there. State law requires a decision on a coastal permit for an ADU within 60 days of a complete application.
Fire hazard zones
The City adopted the state's 2025 fire hazard severity zone maps, effective August 30, 2025. Its map shows only Very High zones, and in them an ADU keeps a 4-foot side and rear setback at any height and bonus ADUs need a street with two evacuation routes. The Fire Code Official can also ask for larger setbacks in the Brush Management Zone.
A homeowners association
An HOA's covenants and rules cannot prohibit or unreasonably restrict an ADU or JADU on a lot zoned for single-family homes; AB 956 extends that, from January 1, 2027, to any lot zoned to allow one. Under the Civil Code such rules are void and unenforceable.
Utilities and sewer
A new ADU needs its own address before SDG&E will take the application, and connection fees and capacity charges follow the state's limits. Where a lot is on septic or the sewer line is far away, plan for that before design.
Next steps
Find your authority, price the ADU, then tell us about the lot.