What it is
A detached ADU is a separate building on the lot, often called a backyard cottage or granny flat, with the most separation from the main house.
The rules
- A city can't set a height limit below 16 feet for a detached ADU (Government Code § 66321(b)(4)).
- Lot-coverage and floor-area rules can't prevent an ADU of at least 800 square feet with four-foot side and rear setbacks (§ 66321(b)(3)).
- No minimum lot size may be required for an ADU (§ 66314(b)(1)).
Summarized from the state's ADU Handbook (HCD). Local rules add details; check with your city before designing.
By the numbers in Los Angeles
The City of Los Angeles issued 2,115 permits for detached ADUs in 2025, 30% of all its ADU permits. That share was 22% in 2020. Of the four ADU types in 2025, detached ADUs were the 2nd most common, the slowest to permit and the highest in declared value. Permits issued in 2025 took a median of 158 days from application (the middle half took 90–301 days). From permit to the city's final sign-off took a median of about 16 months, and 82% of permits issued from 2020 through 2023 have been signed off as finished. Owners declared a median of $109,482 on permits issued in 2025 (middle half $76,200–$150,000). Declared values understate the full cost.
| Year | Detached ADU permits | Share of ADU permits | Median days to permit | Median declared value |
|---|---|---|---|---|
| 2020 | 726 | 22% | 194 | $98,000 |
| 2021 | 1,251 | 25% | 247 | $100,000 |
| 2022 | 1,909 | 27% | 254 | $100,394 |
| 2023 | 1,787 | 29% | 231 | $110,000 |
| 2024 | 1,942 | 30% | 201 | $100,000 |
| 2025 | 2,115 | 30% | 158 | $109,482 |
Where in the San Fernando Valley
The Valley neighborhoods with the most detached ADUs (2020 to date) are North Hollywood (578), Reseda (414) and Northridge (407). As a share of each neighborhood's ADU permits, they are most common in Shadow Hills and Lake View Terrace (41%), Encino (39%) and Sun Valley (38%).
Practical tips
- Utility runs from the house (sewer, water, power) can be a large part of the cost on deep lots.
- Ask about the city's pre-approved standard plans, which can shorten plan check.
- Hillside and fire-zone lots add review and cost: check your lot's designations first.
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