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.
Fullerton (Orange County) reported 168 ADU building permits in 2025, 53% more than the 110 it reported in 2024. That compares with 18 in 2018. The busiest year in this data was 2025, with 168 permits. ADUs made up 27.5% of all new homes permitted in Fullerton in 2025; statewide the figure was about 26%.
ADU permits in Fullerton 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 | 18 | 86 | 20.9% |
| 2019 | 37 | 342 | 10.8% |
| 2020 | 41 | 68 | 60.3% |
| 2021 | 87 | 122 | 71.3% |
| 2022 | 65 | 72 | 90.3% |
| 2023 | 75 | 458 | 16.4% |
| 2024 | 110 | 176 | 62.5% |
| 2025 | 168 | 612 | 27.5% |
ADU rules in Fullerton
We have not yet verified an official ADU page for Fullerton. 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.