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.
Santa Monica (Los Angeles County) reported 143 ADU building permits in 2025, 10% more than the 130 it reported in 2024. That compares with 20 in 2018. The busiest year in this data was 2025, with 143 permits. ADUs made up 31.8% of all new homes permitted in Santa Monica in 2025; statewide the figure was about 26%.
ADU permits in Santa Monica 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 | 20 | 399 | 5.0% |
| 2019 | 60 | 528 | 11.4% |
| 2020 | 40 | 264 | 15.2% |
| 2021 | 81 | 275 | 29.5% |
| 2022 | 133 | 432 | 30.8% |
| 2023 | 127 | 530 | 24.0% |
| 2024 | 130 | 205 | 63.4% |
| 2025 | 143 | 450 | 31.8% |
ADU rules in Santa Monica
We keep a sourced summary of local rules on our Santa Monica ADU rules page. The official source is City of Santa Monica: 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.