Detached vs Attached ADU
Whether your garage is attached to the house or standing on its own changes which unit you can legally build, not just how the job is priced. An attached garage can become either a full ADU or a junior ADU. A detached garage can only become a full ADU, because state law requires a JADU to sit entirely within the residence.
California ADU law was renumbered by SB 477 in March 2024. The sections cited here are the current ones, Gov. Code 66310 to 66342. Local overlays still apply to your parcel, so confirm your specifics with your city building department or San Diego County before finalising plans.
What the rules actually say
- A JADU must be "constructed within the walls of the proposed or existing single-family residence", and state law counts enclosed uses like attached garages as part of that residence (Gov. Code 66333(d))
- A detached garage is not within those walls, so its path is a full ADU
- Converting an existing structure, or rebuilding it in the same location to the same dimensions, requires no new setback (Gov. Code 66314(d)(7))
- A newly built detached ADU is different: a setback of no more than four feet from the side and rear lot lines may be required
- A detached unit usually needs its own utility runs from the house, which is the practical cost difference rather than a legal one
Common questions
Can I convert a detached garage into a junior ADU?
No. State law requires a junior ADU to be contained entirely within the single-family residence, and specifies that enclosed uses such as attached garages count as part of that residence (Gov. Code 66333(d)). A detached, freestanding garage does not meet that test, so it is permitted as a full ADU instead.
Do I need to move the walls back to meet setbacks?
Not for a straight conversion. State law says no setback is required for an existing accessory structure converted to an ADU, or for a structure rebuilt in the same location and to the same dimensions (Gov. Code 66314(d)(7)). Building something new and larger is a different question, and your plan checker will confirm it for your lot.
Is a detached conversion more expensive than an attached one?
Usually, and the reason is utilities rather than law. A detached structure often needs new electrical, water, and sewer runs trenched from the main house, which an attached garage sitting next to the existing plumbing does not. Your crew prices that after seeing where the connections actually are.
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