Attached ADU · City of San Diego
Attached ADUs in San Diego
An attached ADU is a separate home built onto your house, with its own kitchen and bathroom. In the City of San Diego it can be 150 to 1,200 square feet. Unlike a room addition, it's a home of its own that you can rent out.
BHI Builders designs, permits and builds attached ADUs, along with detached ADUs, garage conversions and junior ADUs, across San Diego County's 19 permit authorities, as one team, under California contractor license 738313, issued in 1997.
- 1997Licensed in California sinceCheck the license
- 111Permits on the public record, 2000 to 2025See the projects
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Joined to the house, with its own front door
An attached ADU shares a wall and usually the roofline with the house, but keeps its own entrance, kitchen and bath, and often a small patio of its own.
Right for your lot when
You want to share a wall, a roofline and a utility run with the house, or the lot leaves no room for a separate building.
The wrong choice when
The only place it fits is the front setback or over the house's main drain, or the house's own foundation and framing can't take the connection without rework.
On the call we tell you which type fits your lot, including if the answer is none.
The rules for an attached ADU
| Rule | What applies |
|---|---|
| Size | 150 to 1,200 square feet in the City of San Diego. State law lets a city cap an attached ADU at half the house's floor area, but never below 850 square feet, or 1,000 with more than one bedroom. |
| Height | Within your zone's overall height limit. State law guarantees at least 25 feet, or the house's own zone limit if that's lower, and doesn't require more than two stories. |
| Side and rear setbacks | None for an ADU 16 feet tall or less. Taller than that, 4 feet (or the zone's setback, if less) where it borders a residential lot. In a Very High Fire Hazard Severity Zone, the only kind on the City's fire map, 4 feet at any height. |
| What makes it an ADU | Complete independent living facilities: permanent provisions for living, sleeping, eating, cooking and sanitation. Without them, it's a room addition and part of the main house. |
| Fire sprinklers | Needed only if the house has them. When the house is sprinklered, the attached ADU is too. |
| Rental term | 31 days or longer. Short-term vacation rentals aren't allowed. |
| Owner on site | Not required. The owner doesn't have to live on the property. |
| Fees | The same as any ADU: no impact fees at 750 square feet or less under state law, and no City development impact fees on the first two ADUs at any size. School fees apply from 500 square feet. A room addition pays school fees only when it adds more than 500 square feet. |
| Energy Code | An attached ADU complies as an addition, so solar panels aren't required. New heating is a heat pump, unless the design meets the energy budget another way. |
Outside the City of San Diego, your city or the County sets these rules within state law. Who issues my permit?
What an attached ADU costs
Our calculator's planning range at a plain spec: about 600 square feet, standard finishes, a flat lot and easy access. Your size, site and finishes move it.
$244,301 to $331,021
Questions about attached ADUs
How is an attached ADU different from an addition?
An ADU is a home of its own, with permanent provisions for living, sleeping, eating, cooking and sanitation, and you can rent it out. An addition is more room for your house. They're also charged differently: an ADU gets the ADU fee breaks, and an addition pays school fees once it adds more than 500 square feet.
How big can it be compared with my house?
In the City of San Diego, up to 1,200 square feet whatever your house's size. Elsewhere, a city may cap an attached ADU at half your house's floor area, but it has to allow at least 850 square feet, or 1,000 with more than one bedroom.
Does it need its own entrance?
An ADU made from space inside your house needs its own entrance from outside. For an ADU built onto the house, the City's code asks for complete independent living facilities rather than naming a door, but a home you can't enter on its own is hard to live in and harder to rent, so plan for one.
Can I rent it separately?
Yes, for 31 days or longer. Short-term vacation rentals aren't allowed in ADUs in the City of San Diego.
Do I pay impact fees?
State law bars impact fees on an ADU of 750 square feet or less, and the City of San Diego waives its development impact fees on the first two ADUs on a lot at any size. School fees from 500 square feet, the City's General Plan Maintenance Fee, and water and sewer capacity charges sized to the ADU still apply.
Talk to us about your lot.
Tell us where it is and what you want the ADU to do. We'll walk it with you and tell you what fits.
