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.
Downey (Los Angeles County) reported 146 ADU building permits in 2025, 27% fewer than the 200 it reported in 2024. That compares with 3 in 2018. The busiest year in this data was 2024, with 200 permits. ADUs made up 72.3% of all new homes permitted in Downey in 2025; statewide the figure was about 26%.
ADU permits in Downey 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 | 3 | 87 | 3.4% |
| 2019 | 16 | 41 | 39.0% |
| 2020 | 53 | 58 | 91.4% |
| 2021 | 113 | 116 | 97.4% |
| 2022 | 137 | 154 | 89.0% |
| 2023 | 142 | 155 | 91.6% |
| 2024 | 200 | 218 | 91.7% |
| 2025 | 146 | 202 | 72.3% |
ADU rules in Downey
We have not yet verified an official ADU page for Downey. Start with the city or county planning department, and the state floor in the HCD ADU Handbook, which every California city must follow.
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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.