How big can an ADU be, and how close to the property line?
The California rules on setbacks, size, height and parking, each with its code section.
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How close to the property line can an ADU go?
A new ADU needs side and rear setbacks of no more than four feet. An existing structure converted to an ADU, such as a garage, needs no setback at all. Front setbacks follow local zoning, but a city cannot use them to block a unit of at least 800 square feet.
How big can an ADU be?
A detached ADU can be up to 1,200 square feet. An attached ADU can reach 50 percent of the existing main house. A city may set lower maximums, but not below 850 square feet, or 1,000 square feet for a unit with more than one bedroom.
| Topic | Rule | Source |
|---|---|---|
| Detached ADU, maximum size | 1,200 sq ft | Gov. Code § 66314(d)(5) |
| Attached ADU, maximum size | 50 percent of the existing main house | Gov. Code § 66314(d)(4) |
| Lowest cap a city may set | 850 sq ft, or 1,000 sq ft with more than one bedroom | Gov. Code § 66321(b)(2) |
| Always allowed | At least 800 sq ft with four-foot side and rear setbacks | Gov. Code § 66321(b)(3) |
| Junior ADU, maximum size | 500 sq ft | Gov. Code § 66333 |
| Side and rear setbacks | No more than four feet; none for a converted structure | Gov. Code § 66314(d)(7) |
| Height, detached | 16 feet; 18 feet near major transit, plus 2 feet for roof pitch | Gov. Code § 66321(b)(4) |
| Height, attached | 25 feet, or the height limit of the main house if lower | Gov. Code § 66321(b)(4) |
| Parking | One space per unit or per bedroom at most, whichever is less | Gov. Code § 66314(d)(10) |
How tall can an ADU be?
A city must allow a detached ADU of 16 feet. The limit rises to 18 feet within half a mile of a major transit stop or a high-quality transit corridor, with 2 more feet to match the roof pitch of the main house. An attached ADU can reach 25 feet, or the main house's height limit if lower.
Do I need to add parking?
Often not. A city can require one space per ADU or per bedroom at most, whichever is less, and none when the lot is within half a mile walking distance of public transit. When a garage is converted or demolished for the ADU, the city cannot require replacement parking.
How many units can I add to a single-family lot?
According to the state's ADU Handbook, a lot with a single-family home can combine one ADU converted from existing space, one junior ADU and one new detached ADU. The City of Los Angeles also limits detached ADUs to two stories.
Sources
- California Government Code § 66314
- California Government Code § 66321
- California Government Code § 66323
- California Government Code § 66333
- California Department of Housing and Community Development, Accessory Dwelling Unit Handbook (March 2026)
- City of Los Angeles, Accessory Dwelling Unit Ordinance (Municipal Code Section 12.22 A.33)
Sources checked on . General information, not legal or financial advice. Rules change and each city applies its own standards: we confirm what applies to your lot during the free site assessment.
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