Antioch, CA Accessory Structures: ADU Impact Fees (2026)

50. Rather than charging an ADU the flat per-unit DIF assessed on a new single-family or multifamily unit, the Community Development Department calculates the fee two ways depending on the property type and applies whichever is lower. On a multifamily parcel, the ADU pays either the flat multifamily rate or the product of (square feet of the ADU divided by the average square footage of existing multifamily units on the parcel) times the multifamily rate. On a single-family parcel, the ADU pays either the multifamily rate or the product of (square feet of the ADU divided by square feet of the primary dwelling) times the single-family rate.

60(D)(3) exempts any accessory dwelling unit smaller than 750 square feet from DIFs entirely, meaning most small backyard cottages and converted garages owe nothing toward the city's four impact fee categories. 2(b)(1), which cap impact fees on ADUs statewide and bar them outright on units under 750 square feet; Antioch's ordinance was amended by Ord. 2181-C-S in March 2020 to bring the fee schedule into line with that state mandate. 60(A), and payment is due at issuance of that permit, not at final inspection or occupancy.