What setbacks apply to a detached ADU in California?

No more than four feet side and rear for the by-right unit.

Do conversions need setbacks?

Not for an existing structure converted in the same place and size (Gov. Code § 66314(d)(7)).

Yes, but it cannot block an 800 sq ft unit with four-foot setbacks. Use the size envelope calculator.

Easements can bar building; they are not modeled here.

Pad width = lot width − 2 × side setback. Pad depth = rear yard depth − rear setback − separation. Pad area = width × depth.

Inputs on this tool, in the order they appear on the form.
Input	What it is actually asking
Side and rear setbacks	Your city’s numbers. California caps them at four feet for the by-right detached ADU.
Separation	Distance between buildings required by local code or fire rules.

Including one where the naive answer misleads, which is the example most calculators leave out.

Type the width and four-foot side setbacks. The pad width shows how wide the ADU can be before anything else is considered.

If the pad is under 800, the tool notes the California floor. Other standards cannot block that unit, though height may mean going up.

Separation from the house often costs more depth than the rear setback. Ask your city what it requires.

Do not design to this result without a survey if property lines are uncertain. See land survey.

What setbacks apply to a detached ADU in California?: No more than four feet side and rear for the by-right unit.
Do conversions need setbacks?: Not for an existing structure converted in the same place and size (Gov. Code § 66314(d)(7)).
Does lot coverage matter too?: Yes, but it cannot block an 800 sq ft unit with four-foot setbacks. Use the size envelope calculator.
What about easements?: Easements can bar building; they are not modeled here.

Figures dated 27 October 2026. Last reviewed September 16, 2026.