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.
San Francisco (San Francisco County) reported 171 ADU building permits in 2025, 26% fewer than the 230 it reported in 2024. That compares with 272 in 2018. The busiest year in this data was 2019, with 483 permits. ADUs made up 8.7% of all new homes permitted in San Francisco in 2025; statewide the figure was about 26%.
ADU permits in San Francisco 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 | 272 | 4,678 | 5.8% |
| 2019 | 483 | 4,732 | 10.2% |
| 2020 | 247 | 3,159 | 7.8% |
| 2021 | 320 | 2,221 | 14.4% |
| 2022 | 342 | 2,852 | 12.0% |
| 2023 | 288 | 3,053 | 9.4% |
| 2024 | 230 | 1,072 | 21.5% |
| 2025 | 171 | 1,959 | 8.7% |
ADU rules in San Francisco
We keep a sourced summary of local rules on our San Francisco ADU rules page. The official source is SF Planning: Accessory Dwelling Units.
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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.