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

18(a) draws a hard line at 750 square feet. Below that size, no impact fee applies at all: the code defines 'impact fee' here as a fee under the state Mitigation Fee Act (Government Code Section 66000(b)) or the Quimby Act (Government Code Section 66477), specifically excluding water and sewer connection fees or capacity charges, which are addressed separately. For an ADU at or above 750 square feet, the City may still charge an impact fee, but it must be prorated: the fee is calculated proportionately based on the ADU's square footage relative to the square footage of the primary dwelling unit on the lot, not as a flat per-unit charge.

18(b). If the ADU is built alongside a new single-family home, the applicant must pay the normal connection fee and capacity charge for a new dwelling. Converted ADUs and JADUs, along with ADUs built under Government Code Section 66323, are exempt from needing a new or separate utility connection and from any related connection fee or capacity charge. All new detached ADUs otherwise need their own utility connection, though the City can waive that if it is itself the utility provider. Any utility connection fee must be proportionate to the burden the ADU places on the water or sewer system, measured by floor area or drainage-fixture units under the Uniform Plumbing Code, and the City's portion of that charge cannot exceed the reasonable cost of providing the service.

These fee limits track state ADU law and prevent the City from using impact and utility fees to price small accessory units out of feasibility.