State law · checked Oct 18, 2026
What California lets cities charge for an ADU
The rules that shape every fee on this site, each quoted from the official text. Local rules can be more generous than these, never stricter.
Gov. Code §66311.5(c)(1)
No impact fees at 750 sq ft or less
A local agency, special district, or water corporation shall not impose any impact fee upon the development of an accessory dwelling unit that has 750 square feet of interior livable space or less or a junior accessory dwelling unit that has 500 square feet of interior livable space or less.
An ADU of 750 sq ft or less of interior livable space, or a JADU of 500 sq ft or less, pays no impact fees: no park, traffic, police, fire, library or similar development fees. Every city, county and special district has to follow this.
Gov. Code §66311.5(c)(1)
Above 750 sq ft: proportional to the main home
Any impact fees charged for an accessory dwelling unit that has more than 750 square feet of interior livable space shall be charged proportionately in relation to the square footage of the primary dwelling unit.
Above 750 sq ft, an impact fee charged per home has to be scaled by the ADU’s size relative to the main home. Fees already charged per sq ft scale by themselves. Our calculator applies this to per-home fees as ADU sq ft ÷ main-home sq ft.
HCD ADU Handbook (March 2026)
The state’s worked example
For example, a 2,000 square-foot primary dwelling with a proposed 1,000 square-foot ADU could result in 50 percent of the impact fee that would be charged for a new primary dwelling on the same site.
This is where our default comes from: unless you enter your main home’s size, we assume 2,000 sq ft and label it as an example.
Gov. Code §66311.5(c)(2)
Water and sewer connection charges aren’t impact fees
“Impact fee” does not include any connection fee or capacity charge charged by a local agency, special district, or water corporation.
The 750 sq ft rule doesn’t cover utility connection or capacity charges. Separate rules in the same section limit them: no new connection for most conversions inside existing space, and a proportionate charge for new detached units.
Ed. Code §17620; Gov. Code §66311.5(c)(3)
School fees start at 500 sq ft
ADUs and JADUs that are less than 500 square feet of interior livable space are not subject to school impact fees.
School districts can charge their developer fee on ADUs of 500 sq ft or more. The fee is per sq ft and is capped by the State Allocation Board’s Level 1 rate unless a district qualifies for a higher level.
State Allocation Board, January 28, 2026
The 2026 Level 1 school fee cap: $5.38 per sq ft
Residential $4.79 $5.17 $5.38
The State Allocation Board raised the residential Level 1 maximum to $5.38 per sq ft (from $5.17). When we haven’t confirmed a district’s own rate, we show this cap as an upper bound, labeled “Up to”.
SB 1117 (Chapter 809, Statutes of 2026)
Starting January 1, 2027: only the area over 750 sq ft
This bill would require the charge for certain accessory dwelling units to be based only on the area in excess of 750 square feet of interior livable space.
SB 1117 was approved on September 29, 2026 and, as a regular statute, takes effect January 1, 2027. A 1,000 sq ft ADU would then pay impact fees on 250 sq ft, not 1,000. Our calculator has a 2027 toggle; where a city’s fee is a fixed per-ADU amount, the 2027 figure is our own estimate and is labeled that way.
Gov. Code §66314
Size: detached ADUs can be capped at 1,200 sq ft
The total floor area for a detached accessory dwelling unit shall not exceed 1,200 square feet.
Many cities allow the full 1,200 sq ft; some set a lower cap (still at least 850 sq ft, or 1,000 sq ft with more than one bedroom).
Gov. Code §66321
Height: at least 16 feet
A height of 16 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit.
Cities must allow at least 16 ft for a detached ADU, 18 ft near major transit (plus 2 ft to match the roof pitch), and 25 ft (or the zone’s limit, if lower) for an attached ADU.
Gov. Code §66314
Setbacks: no more than 4 feet
a setback of no more than four feet from the side and rear lot lines shall be required for an accessory dwelling unit that is not converted from an existing structure
Side and rear setbacks for a new ADU can’t exceed 4 ft. A garage or shed converted in place needs no added setback.
Gov. Code §66314
Parking: one space at most
Parking requirements for accessory dwelling units shall not exceed one parking space per accessory dwelling unit or per bedroom, whichever is less.
And none at all in many cases, including within half a mile of public transit.
Gov. Code §66317
A decision within 60 days
The permitting agency shall either approve or deny the application to create or serve an accessory dwelling unit within 60 days from the date the permitting agency receives a completed application
Once an application is complete, the city or county has 60 days to approve or deny it.
This is a plain-English summary, not legal advice. The statute is the authority; follow the links to read it in full.