What the rules allow
ADU rules come from the state and the city. Some states set floors every city must follow; others leave it to each city. Two examples.
California
State law sets the floor- ADUs approved ministerially (staff-level) in residential and mixed-use zones.
- No minimum lot size; side and rear setbacks no more than 4 ft for new ADUs.
- Maximum size can't be set below 850 sq ft, or 1,000 sq ft with more than one bedroom.
- At most one parking space per unit, and none for some, such as units within half a mile of transit or conversions.
- No impact fees on ADUs under 750 sq ft.
- A junior ADU (JADU) inside the house: up to 500 sq ft, one per lot.
- Decision within 60 days.
Gov. Code §§ 66310–66342. HCD Housing Law Fact Sheet, April 2026.
Florida
Up to each city- State law lets a local government adopt an ordinance allowing ADUs in single-family zones; it doesn't require it.
- For units approved under that statute, the applicant signs an affidavit that the unit will be rented at an affordable rate.
- The statute sets no size limits.
- Many cities and counties also have their own ADU or "guest house" rules, so check your zoning code.
Ask your planning department
Bring these to the counter or the first call. The answers decide what fits.
- Are ADUs allowed in my zone, detached and attached?
- What are the side and rear setbacks for an ADU?
- What's the maximum size and height?
- Is parking required, and is my lot near transit?
- Do I have to live on the property?
- Can the unit be rented, and for how short a stay?
- Which impact or utility fees apply?
- Are there easements or utility lines in my backyard?