What an ADU costs in San Diego

Total cost by ADU type

There's no official source for what ADUs cost, so the best numbers are the prices San Diego builders publish. Snap ADU, one of the most active builders in the city, lists these all-in prices for a detached ADU on a level lot:

Smaller units cost more per square foot because the kitchen, bathroom, utilities and permits cost about the same whatever the size. A second detached unit built at the same time costs about 85% of the first. Building costs have risen fast: Snap ADU cites a 44% rise in California's construction cost index from 2021 to 2025, so treat older prices with care.

What a price should include

Quotes are hard to compare because builders draw the line in different places. Snap ADU's base price, for example, includes:

• design and construction drawings, including structural and energy (Title 24) reports,
• handling the permit application,
• basic site work on a level lot (about $35,000: trenching, utility hookups, grading), and
• standard finishes.

It leaves out city, school and sewer fees, demolition, retaining walls, extra grading, a separate electric meter and premium finishes. When you compare bids, ask each builder to list what's excluded in writing. Our hiring guide covers what the contract must say.

City and utility fees

The City of San Diego's fees rise with the size of the unit. Snap ADU's published fee table (February 2026) adds up the plan check, building permit, water and sewer capacity and other city charges to:

The jump at 500 square feet comes from plan check and permit fees roughly doubling above that size, plus school fees. Confirm current fees with the city's Development Services Department before you budget; these are a builder's figures, not the city's schedule.

• Development impact fees: San Diego exempts the first two ADUs on a property, whatever their size. State law separately bans impact fees on any ADU of 750 square feet or less.
• School fees: San Diego Unified charges $5.38 per square foot of new living space. ADUs under 500 square feet are exempt under state law. Other school districts set their own rates.
• Water meter: if your ADU gets its own water meter, expect a San Diego County Water Authority capacity charge of several thousand dollars on top of city fees.

What makes your lot cost more

Site conditions are where budgets most often slip. Snap ADU's San Diego figures:

Properties in the coastal zone usually need a Coastal Development Permit, and lots in high fire hazard zones can need fire-rated windows and eaves.

Ways to spend less

• Stay at or under 750 square feet to stay clear of impact fees anywhere in California, or under 500 to avoid school fees.
• Use a pre-approved plan. The City of San Diego accepts the County of San Diego's, Chula Vista's and Encinitas's pre-approved plans. Builders estimate this saves $6,000–$8,000 in design, and cities must decide within 30 days.
• Convert before you build. A conversion avoids most site work, though an old garage can need so much work that rebuilding is cheaper.
• Get three bids on the same plans so the prices are comparable.

Paying for it

Most homeowners pay with a home equity line of credit, a home equity loan, a cash-out refinance or a construction loan. Fannie Mae's HomeStyle Renovation and Freddie Mac's CHOICERenovation loans can roll the cost of a new ADU into one mortgage.

The San Diego Housing Commission has offered construction loans of up to $250,000 to eligible homeowners who rent the ADU at an affordable rent; check whether it's currently funded. The state's CalHFA ADU grant of up to $40,000 has been fully reserved since December 2023.

Rent and property tax

Snap ADU estimates a 750-square-foot, two-bedroom ADU in San Diego rents for about $3,500 a month. For comparison, the average one-bedroom across the city listed for about $2,400 in August 2026. There's no reliable public dataset of ADU rents, so check listings near you.

Building an ADU doesn't reassess your whole home. The county adds only the value of the new construction to your assessment, usually with a supplemental tax bill when it's finished.

Common questions