What is an ADU? An ADU (accessory dwelling unit) is a small second home on the same lot as a house, with its own kitchen and bathroom. Granny flats, in-law units, backyard cottages and garage conversions are all ADUs. More on what counts.
Unincorporated San Diego County (San Diego County) reported 400 ADU building permits in 2025, 18% fewer than the 488 it reported in 2024. That compares with 79 in 2018. The busiest year in this data was 2024, with 488 permits. ADUs made up 46.1% of all new homes permitted in Unincorporated San Diego County in 2025; statewide the figure was about 26%.
ADU permits in Unincorporated San Diego County by year
Source: HCD Housing Element Annual Progress Report, Table A2 (data.ca.gov) checked Oct 2026. Our count, see method.
| Year | ADU permits | All homes permitted | ADU share |
|---|---|---|---|
| 2018 | 79 | 728 | 10.9% |
| 2019 | 137 | 862 | 15.9% |
| 2020 | 142 | 623 | 22.8% |
| 2021 | 299 | 1,425 | 21.0% |
| 2022 | 338 | 1,511 | 22.4% |
| 2023 | 423 | 1,154 | 36.7% |
| 2024 | 488 | 919 | 53.1% |
| 2025 | 400 | 867 | 46.1% |
ADU rules in Unincorporated San Diego County
Official rules: County of San Diego PDS: ADU Information checked Oct 2026. State law sets the floor; see the HCD ADU Handbook.
We connect you with builders from this directory who serve your area. Free, no obligation.
Method
- Counts are building permits for units the jurisdiction reported as ADUs, with an issue date in the report year, after removing exact duplicate rows. Same method as our California ADU Data page.
- Permits are not finished homes. 2025 filings were due in April 2026, and late or corrected filings can change the numbers.