The four kinds of ADU
An accessory dwelling unit (ADU) is a second, independent home on a lot with a house or apartment building. California law recognizes several kinds:
- Detached ADU
- A separate building, often called a backyard cottage or granny flat. State law does not let a city cap its height below 16 feet (Government Code § 66321), and front setbacks cannot prevent an ADU of at least 800 square feet.
- Attached ADU
- A new unit attached to the main house, such as an addition, with its own entrance.
- Garage conversion
- An existing garage turned into a living unit. A city may not require the lost parking to be replaced when a garage is converted to an ADU (Government Code § 66314).
- Junior ADU (JADU)
- A unit of no more than 500 square feet, entirely within a single-family home, for example a converted bedroom with an efficiency kitchen. It can have its own bathroom or share the house's (Government Code § 66313). If it shares, the owner must live in the house or the JADU (§ 66333); regular ADUs have no owner-occupancy requirement (§ 66315).
Summarized from the state's ADU Handbook (HCD). Local rules add details; check with your city before designing.
In depth: Garage conversion ADUs in Los Angeles, Junior ADUs (JADUs) in Los Angeles, Detached ADUs in Los Angeles.
How they compare in Los Angeles (2025)
| Type | Share of ADU permits | Median days to permit | Median declared value |
|---|---|---|---|
| Garage conversion | 38% | 103 | $50,000 |
| Junior ADU (JADU) | 10% | 72 | $35,000 |
| Attached ADU | 17% | 135 | $65,000 |
| Detached ADU | 30% | 158 | $109,482 |
Types are classified automatically from permit descriptions; a few percent are unclassified. Declared values understate real cost.
What people are building
Garage conversions were 57% of Los Angeles ADU permits in 2020 and 38% in 2025; junior ADUs went from 4% to 10%. See the San Fernando Valley ADU report for how this varies by neighborhood.
Which is right for you?
- Fastest and usually cheapest: a junior ADU or garage conversion reuses an existing structure.
- Most privacy and space: a detached ADU, at the highest cost and the longest permit time.
- Keep your garage: an attached or detached ADU.
What fits depends on your lot, zoning and any hillside or fire-zone rules. LA Department of Building and Safety or a licensed builder can tell you what your property allows.
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