The short answer
State law waives most fees for a small ADU. An ADU with 750 square feet of interior living space or less (or a junior ADU of 500 or less) owes no impact fees, and one under 500 square feet owes no school fees. What everyone pays is the city's plan check and building permit fees, which are based on the project's value. Bigger units add school fees and impact fees, and a new detached unit can owe utility connection charges (Government Code § 66311.5).
What state law allows, by size
| Fee | Under 500 sq ft | 500 to 750 sq ft | Over 750 sq ft |
|---|---|---|---|
| Impact fees (including park fees) | None | None | In proportion to the house's size |
| School fees | None | The district's rate (standard cap $5.38 per sq ft) | The district's rate (standard cap $5.38 per sq ft) |
| Utility connection and capacity charges | None in existing space; proportionate otherwise | None in existing space; proportionate otherwise | None in existing space; proportionate otherwise |
| Plan check and building permit | Yes | Yes | Yes |
Sizes are interior living space. At exactly 500 square feet the school-fee rule is unclear; ask your school district. A junior ADU (500 square feet or less, inside the house) owes no impact fees.
The rules behind the table
- Impact fees. None on an ADU of 750 square feet of interior living space or less, or a JADU of 500 or less. Above that, a city may charge them only in proportion to the size of the main house. Park fees count as impact fees; utility connection fees don't (§ 66311.5(c)).
- School fees. An ADU or JADU under 500 square feet of interior living space owes none (§ 66311.5(c)(3)). Above 500, school districts may charge them. The standard (Level 1) cap, set by the State Allocation Board, is $5.38 per square foot since January 28, 2026; districts that have adopted a facilities needs study can charge more (Level 2 or 3), and some charge less or exempt ADUs. Ask your district for its rate.
- Utilities. An ADU or JADU isn't a new residential use for connection fees or capacity charges unless it's built with a new house (§ 66311.5(b)). One in existing space can't be made to add a new utility connection or pay those charges, unless it's built with a new house or sold separately (§ 66311.5(d)). Other ADUs, such as a new detached one, can be required to connect separately, but the charge must be proportionate to the unit's size or plumbing fixtures and not more than the reasonable cost of service (§ 66311.5(e)).
The 750-square-foot impact fee exemption dates from 2020. Since January 1, 2026 (SB 543) it's measured as interior living space, it covers junior ADUs of 500 square feet or less, and the rules moved from § 66324 to § 66311.5.
Coming January 1, 2027
SB 1117, signed September 29, 2026, changes how impact fees on an ADU over 750 square feet are figured: they may be charged only on the area above 750 square feet, instead of in proportion to the size of the house.
Los Angeles
- Park and linkage fees: the city says ADUs and JADUs are exempt from its park fee and Affordable Housing Linkage Fee (Zoning Administrator Memo 143, revised August 1, 2025).
- Plan check and permit fees are calculated from the project's valuation, with surcharges added. LADBS has an online permit fee calculator.
- School fees: LAUSD charges $5.38 per square foot for new residential space (effective August 11, 2026), for ADUs over 500 square feet.
- Sewer: a new detached ADU can owe the city's Sewer Facilities Charge, based on the sewage it's expected to add; state law requires the charge to be proportionate.
- Electricity: LADWP generally serves a lot through one service. A separate meter for the ADU needs its own legal address.
Ventura County
Each city sets its own permit fees, and school fees depend on the district. What official pages say:
- Ventura Unified School District: School fees of $5.38 per square foot (its page, as of June 20, 2026).
- Conejo Valley Unified School District: School fees of $3.36 per square foot; its page exempts ADUs of 750 square feet or less and JADUs of 500 or less.
- Oxnard School District: School fees of $2.75 per square foot for the elementary district; the Oxnard Union High School District charges its own share.
- Camarillo: A $174.46 zone clearance; school fees for ADUs of 500 square feet or more; building fees carry a 17.89% general plan maintenance surcharge and an 11.34% technology surcharge (since July 1, 2025).
- Thousand Oaks: Building fees averaged $2,800 to $3,200 per ADU over the past three years, plus planning and connection fees, and impact fees on ADUs over 750 square feet (the city, the school district, Ventura County Fire, and the Conejo Recreation and Park District).
- City of Ventura: Reduced review fees for ADUs built from its free pre-approved plans.
- Unincorporated Ventura County: Reduced review fees for ADUs built from its free pre-approved plans.
For other cities and school districts, ask the city's planning or building department; our Ventura County application guide links each one's ADU page.
Lots that need extra review
Coastal Zone lots need a coastal development permit or exemption, decided within 60 days since October 10, 2025 (Government Code § 66329); in Los Angeles, ZIMAS shows whether a parcel is in the Coastal Zone, and statewide the Coastal Commission has boundary maps. Unincorporated Ventura County doesn't allow junior ADUs in its Coastal Zone until its updated coastal zoning is certified. Hillside and fire-zone lots in Los Angeles can face extra conditions; see hillside, fire-zone, historic and coastal lots.
Budgeting for fees
- The ADU cost estimator works out school and impact fees for your size and area.
- Ask your city for a fee estimate for your exact design before you commit; fees depend on size, valuation and location.
- Keep the unit at 750 square feet of interior living space or less to avoid impact fees, and under 500 to avoid school fees, if the design works for you.
- Make sure builder quotes say which fees they include.
See also: California ADU rules, pre-approved ADU plans, how to pay for an ADU, what ADUs cost in Los Angeles, choosing a licensed builder.
Summarized from the statutes, the state's ADU Handbook (March 2026) and each agency's page as checked on September 29, 2026. Fee amounts change, often every year; confirm them with your city and school district.
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