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California ADU requirements – size, setbacks and permit plans

California ADU rules in plain English: sizes, 4 ft setbacks, height limits, JADUs, parking and the drawings your city needs for a permit.

Reading time about 7 minutes

Why California is different

California has statewide ADU laws. Every city must allow ADUs on lots with a single-family home and approve a complete application within 60 days. Cities can add their own rules, but they can't go below the state minimums.

Key numbers

Values to plan with:

Main houseUsually 16 ftDetached ADUUp to 18–25 ft in some cases4 ft
Typical state minimums for a detached ADU. Example only – check your city.
  • Detached ADU: cities must allow at least 800 sq ft, often up to 1,000–1,200 sq ft.
  • Attached ADU: often capped at 50% of the main house, but at least 800 sq ft must still be allowed.
  • Smallest ADU: about 150 sq ft (an efficiency unit).
  • Side and rear setbacks: no more than 4 ft can be required.
  • Height: at least 16 ft; more near transit or to match the main roof.
  • Junior ADU (JADU): up to 500 sq ft inside the existing home, with its own outside door; it may share a bathroom with the main house.
  • Impact fees: usually waived for ADUs under 750 sq ft.
  • Parking: often not required, for example within half a mile of transit.

Drawings for the permit

Most cities want a site plan with setbacks and utilities (often 1" = 20'), a floor plan at 1/4" = 1'-0", all four elevations and a section. Structural, energy (Title 24) and utility sheets are usually added by professionals.

1/4" = 1'-0"Site plan1/4" = 1'-0"Floor plan1/4" = 1'-0"Elevations1/4" = 1'-0"Section
The core sheets most California cities ask for.

Rules that protect homeowners

State law gives you a lot of support:

  • No minimum lot size: a small lot alone can't stop an ADU.
  • Your HOA can set design rules, but generally can't ban an ADU.
  • Fire sprinklers aren't required in the ADU unless the main house already has them.
  • Approval is ministerial: no public hearing, and no 'doesn't fit the neighborhood' denials. Plans that meet the clear, written standards must be approved.
  • Long-term renting is allowed. A regular ADU has no owner-occupancy rule, but with a JADU the owner must live on the property.
  • Only the new ADU's value is added to your property tax – the main house isn't reassessed.

Help paying for plans

The CalHFA ADU Grant Program has offered up to $40,000 toward pre-development costs such as drawings, permits and site work. Funding comes in rounds and has rules on income, so check calhfa.ca.gov for the current status before you count on it.

Frequently asked questions

Can I have both an ADU and a JADU?

Yes. State law generally allows one detached ADU and one JADU on a single-family lot.

Do I need an architect?

California doesn't require one for most single-family ADUs, but structural and energy calculations often need a licensed professional.

Can my HOA block an ADU?

Generally no. An HOA can set reasonable design rules, but California law stops it from banning ADUs on single-family lots.

Do I need fire sprinklers in the ADU?

Not unless the main house already has them. Check fire access and wall separation with your city.

Codes and zoning vary by state, county and city. Always check with your local building department and HOA before you build.

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