Checker · state law as of Oct 18, 2026

Can I build an ADU?

Tell us about your lot and the ADU you have in mind. We show what California law guarantees for it, quoting the Government Code section behind each answer. Your city can be more generous, never stricter.

What’s on the lot now (or planned)? A single-family home A multifamily building (duplex, apartments)

What kind of ADU? Detached (backyard cottage) Attached addition Conversion of existing space (garage, basement) Junior ADU (inside the house, up to 500 sq ft)

ADU size (interior livable sq ft) optional

Main house size (sq ft) optional

Matters for attached ADUs, which a city may limit to half the main house.

Lot size (sq ft) optional

Bedrooms in the ADU Studio or 1 bedroom 2 or more Not sure yet

Within a half-mile walk of transit? Yes No Not sure

City or county optional

Not legal advice

This checker summarizes state minimums in Government Code, Title 7, Division 1, Chapter 13 (Accessory Dwelling Units), incl. §66311.5. It doesn’t know your zoning, easements, fire zone, historic status, HOA rules or utilities, and it can’t tell you whether a permit will be approved. Read your city’s ADU ordinance and talk to its planning counter before you design or spend money.

State law, quoted in full →