State rules (apply everywhere in California)
- Size. Local limits must allow an ADU of at least 850 square feet, or 1,000 square feet if it has more than one bedroom.[1]
- Setbacks. Cities can't block an 800 square foot ADU with four-foot side and rear setbacks.[1]
- No owner-occupancy rule for ADUs. A junior ADU (JADU) that shares a bathroom with the main house does require the owner to live there.[1]
- JADUs are up to 500 square feet and built inside the existing house.[1]
- Unpermitted ADUs built before January 1, 2020 can't be denied a permit just for violating building standards or ADU rules (AB 2533).[1] That's a big deal if the house you're buying has an old garage conversion.
City of San Diego
- ADUs can now become separate condominiums that can be sold on their own, except ADUs built under the ADU Home Density Bonus Program or funded by the San Diego Housing Commission.[2]
- The ADU Home Density Bonus Program is no longer allowed in several single-family zones unless the site is in a high-resource area. On lots up to 8,000 square feet, it's capped at 4 ADUs.[2]
Unincorporated San Diego County
- The County's ADU fee waiver ended on January 9, 2024.[3]
- The County adopted the ADU condo option (AB 1033), effective April 4, 2026.[4]
Buying a house with an ADU, or one with room for one? I'll pull sales of similar homes so you know what the ADU is actually worth.
Related questions
Do I have to live on the property to rent out an ADU?
No. State law bars owner-occupancy rules for ADUs. The exception is a junior ADU that shares a bathroom with the main house.
Can I sell an ADU separately in San Diego?
In the City of San Diego, yes, since August 22, 2025 (outside the Coastal Zone), by converting it to a condo. Density-bonus and Housing Commission-funded ADUs are excluded. Unincorporated County areas allow it since April 4, 2026.
What if a house has an unpermitted ADU?
Under AB 2533, an ADU built before January 1, 2020 can't be denied a permit just for building-standard or ADU-rule violations. Ask the city what it would take to permit one before you buy.
How big can an ADU be in California?
Local limits must allow at least 850 square feet, or 1,000 for more than one bedroom. Without a compliant local ordinance, the state default for a new detached ADU is 1,200 square feet.
Is a house with an ADU a better investment than new construction?
It depends on the rent the ADU can earn and the price gap. Text me the two homes and I'll pull comparable sales and rents for both.
Related answers, guides and reports
Still have a question?
Text me at (559) 977-2596. I answer every one myself, no pressure and no sales pitch.
Sources
- California HCD ADU Handbook (March 2026)
- City of San Diego: 2025 ADU and JADU amendments
- County of San Diego: ADUs (unincorporated areas)
- County of San Diego: AB 1033 ADU condo amendment
Payment math is an estimate, not a loan offer. Talk to a lender for your actual numbers. Josiah Garcia | Real Broker | DRE #02128093.