Published · By Jeff Brick, 2026 SDMLS President
Quick answer: In the City of San Diego, most single-family lots can add one accessory dwelling unit (ADU) plus one junior ADU, up to 1,200 square feet, with no parking required, and the city must decide on a complete application within 60 days. ADUs of 750 square feet or less are exempt from impact fees under state law. A peer-reviewed study of Los Angeles found an ADU raises a property’s selling price by about 7% to 9%, and here a new studio or one-bedroom ADU competes in a market where the average one-bedroom rents for $2,350 a month. The real question for investors is whether your build cost, financing and rent pencil out on your specific lot.
This is general information, not legal, tax or financial advice. Confirm your project with the City of San Diego Development Services Department, a licensed architect or contractor, your lender and your CPA.
Why ADUs matter for San Diego investors right now
Granny flats are no longer a niche project. According to the City of San Diego’s 2025 Annual Report on Homes, the city permitted 2,285 ADU homes in 2024, about 26% of the 8,782 homes permitted that year and the most in a single year. That share was 17% in 2021, 12% in 2022 and 20% in 2023.
For investors, that tells me two things: the permitting path is well worn, and you will be competing with a lot of other small rentals. Good design and a smart floor plan matter more than ever. If you are weighing an ADU against buying a small condo to rent, my San Diego condo gap guide for investors walks through the other side of that decision.
San Diego ADU rules: the short version
State law sets the floor, and the city layers its own rules on top. Here is what matters most, based on the California HCD ADU Handbook and the City of San Diego ADU/JADU page.
How many units and how big
- Single-family zones: one ADU and one junior ADU (JADU). A JADU must sit inside the existing or proposed house or an attached garage.
- Multifamily zones: up to two detached ADUs, plus conversions of non-living space in existing buildings.
- Size: the city allows up to 1,200 square feet, attached or detached. State law guarantees at least an 800-square-foot detached ADU with four-foot side and rear setbacks.
- Height (state standard): 16 feet for most detached ADUs, 18 feet near a major transit stop, and up to 25 feet for attached ADUs (or the home’s height limit, if lower).
Parking, timing and owner occupancy
- Parking: the city requires none, and you do not have to replace garage parking when you convert a garage.
- Timing: once an application is complete, the city must approve or deny it within 60 days (state law).
- Owner occupancy: state law bars owner-occupancy requirements on ADUs (AB 976). JADUs that share a bathroom with the main house are the exception.
- Rentals: the city treats ADUs as permanent housing, so rental terms must be at least 31 consecutive days. Plan for long-term tenants, not Airbnb.
What changed in 2025
In June 2025 the City Council adopted 25 reforms to its ADU rules, as reported by the city’s Inside San Diego news site. Highlights: ADUs can now be split off and sold as condominiums under AB 1033; the ADU Home Density Bonus Program was barred in most of the lowest-density single-family zones (with exceptions in high-resource areas) and capped by lot size; bonus ADUs outside Transit Priority Areas need one parking space each; and smaller bonus units pay a Community Enhancement Fee. In the Coastal Zone, these changes need California Coastal Commission certification, so check the status if your lot is near the coast.
What an ADU costs in San Diego
Fees
Fees are where San Diego is friendlier than many cities. The city waives Development Impact Fees, Facility Benefit Assessment fees and General Plan Maintenance fees for ADUs. State law also bars impact fees on ADUs of 750 square feet or less and requires fees on larger ADUs to be proportional to the main home’s size, according to the HCD ADU Handbook. School fees and water and sewer connection charges can still apply, so get those numbers early.
Construction
Build costs vary more than anything else in this equation. The most-cited statewide benchmark, a UC Berkeley Terner Center survey of ADU owners, found a median cost of $150,000, or $250 per square foot, but that survey was published in April 2021 and costs have risen since. Treat it as a floor, not a quote. Garage conversions and attached units usually cost less than new detached builds, and hillside lots, long utility runs and fire-zone requirements push costs up. I recommend getting at least two or three bids before you run your numbers.
Property taxes
Under California’s Prop 13 system, an ADU is assessed like an addition: the assessor adds the market value of the new construction to your existing assessment. As one county assessor explains, “The existing home will not be reassessed.” Expect a supplemental tax bill for the new square footage only.
What an ADU adds to value and income
Resale value
The best research I have seen comes from UC Irvine economists Jan Brueckner and Sarah Thomaz, published in Real Estate Economics (2024). Studying Los Angeles, they found an ADU raises a property’s assessed value and selling price by about 7% to 9%. That is Los Angeles, not San Diego, but it is a sensible starting point. In my experience, a permitted, well-designed ADU with its own entry and outdoor space draws a wider buyer pool: multigenerational families, buyers who want help with the mortgage, and investors.
Rental income
Most ADUs here are studios and one-bedrooms. According to Zillow Rental Manager (updated October 15, 2026), San Diego’s average rent is $1,995 for a studio, $2,350 for a one-bedroom and $3,132 citywide, up $47 from a year earlier. A new ADU with a private yard may earn more or less than those averages depending on location, finishes and parking.
A simple way to run the numbers
- Total project cost = bids + design + permits + school and utility fees + a 10% to 15% contingency.
- Annual net rent = (expected monthly rent × 12) − vacancy, insurance, maintenance and the added property tax.
- Yield = annual net rent ÷ total project cost. Compare that with your financing cost and with what the same money could earn elsewhere.
- Then add the resale bump as a bonus, not as the reason to build.
For renters: ADUs add small, often quieter rental homes in established neighborhoods. Ask whether the unit is permitted and whether utilities are separately metered before you sign.
Jeff’s take
I love a good ADU, especially behind a craftsman in North Park or a Spanish-style home in Kensington, where a thoughtful backyard cottage can honor the main house instead of fighting it. But I tell investors the same thing every time: build it because the rent and the cost work, not because a headline promised a huge value bump. Start with the lot, the utilities and three real bids. As a San Diego REALTOR® at Compass, President of the San Diego Multiple Listing Service, a Board Director of the San Diego Association of REALTORS® and the largest luxury apartment home leasing broker in Southern California, I watch the rental side of this market every day, and I am happy to help you size up a property with ADU potential before you buy.
Thinking about an ADU property?
Whether you want to buy a home with a permitted ADU, add one to a property you own, or sell a home with ADU upside, let’s talk. Call or text me at 858-324-4448 or reach out through jeffbrick.com. Million Dollar Service at All Price Points.
FAQ: ADUs in San Diego
Can I build an ADU on my San Diego lot without parking?
Yes. The City of San Diego requires no parking for ADUs and no replacement parking when a garage is converted. Bonus ADUs under the density bonus program outside Transit Priority Areas are an exception after the 2025 reforms.
How big can an ADU be in San Diego?
Up to 1,200 square feet, attached or detached. A JADU is limited to 500 square feet and must be inside the main home or an attached garage.
Do I have to live on the property?
No. State law (AB 976) bars owner-occupancy requirements for ADUs. A JADU that shares a bathroom with the main home is the exception.
Can I rent my ADU on Airbnb?
Not short-term. The city requires ADU rentals of at least 31 consecutive days.
Will an ADU raise my property taxes?
Only for the new construction. The assessor adds the ADU’s value to your current assessment, and the existing home is not reassessed.
About the author: Jeff Brick is a San Diego REALTOR® at Compass (DRE# 02156850), 2026 President of the San Diego Multiple Listing Service, a 2024–2026 Board Director of the San Diego Association of REALTORS®, and the largest luxury apartment home leasing broker in Southern California.
