Guide · impact fees
An ADU with 750 square feet or less of interior livable space is exempt from every impact fee in California, and a JADU of 500 square feet or less is exempt too. Above 750 square feet, impact fees must be charged in proportion to the size of your main house, not at the flat rate a new home would pay. The rule is Gov. Code § 66311.5(c)(1), and it was renumbered in January 2026, so fee schedules citing “§ 66324” are quoting a section that no longer exists.
“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. 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.”
Gov. Code § 66311.5(c)(1) · verified against leginfo
Impact fees are the charges cities levy on new development for its load on public facilities: school fees, park fees, traffic mitigation. On a new house they commonly run to five figures. Under 750 square feet, none of them may touch your ADU.
The exemption covers impact fees, not service charges. Plan check, the building permit itself, inspections, and utility work are payment for services actually rendered and remain due at any size. When a quote arrives as a single number, ask for it itemized against the city's published fee schedule: the exemption is only auditable line by line, and cities publish those schedules. Where we hold a city's schedule, it appears on that city's builders page in the city's own wording.
State law guarantees you the right to build an 800 square foot ADU (Gov. Code § 66323), but only exempts 750 square feet from impact fees. Between those two numbers, every fee the city charges switches on at once. If your design is hovering near the line, the 50 square feet between 750 and 800 are likely the most expensive floor area you can buy, and a 749 square foot plan is worth pricing against the 800 square foot one before you commit either way.
For junior ADUs the statute is explicit: for water, sewer, or power, “including a connection fee, a junior accessory dwelling unit shall not be considered a separate or new dwelling unit” (Gov. Code § 66338). For full ADUs, connection and capacity charges depend on how the unit was created, and for pre-2020 unpermitted units being legalized they are barred outright under § 66311.7. Get the utility's demand in writing before you accept any number in a contractor's allowance.
This exemption lived at § 66324 until SB 543 renumbered it to § 66311.5 effective January 1, 2026, and before 2024 the whole ADU chapter lived at § 65852.2. A city fee schedule or consultant memo citing those numbers predates the current text. The figures may still be right, but the citation no longer resolves, and a schedule that has not been re-checked against the renumbered chapter deserves scrutiny on its substance too. Verify any citation with the citation checker.
The rules above are the statewide floor. What you can build also depends on your jurisdiction's compliance status and your lot. The feasibility check resolves both and returns a size range with the governing section for every figure.