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

320(4)(B) sets Hercules's ADU fee structure in 3 tiers. First, ADUs of 750 square feet or more are subject to whatever residential-unit fees the City's Master Fee Schedule sets at the time the application is filed, but those fees must be charged in proportion to the ADU's square footage relative to the primary dwelling; the code gives its own example, that a 1,000-square-foot ADU on a lot with a 2,000-square-foot primary home is charged 50 percent of the applicable fee. ADUs on single-family lots pay single-family unit fees while ADUs on multifamily lots pay multifamily unit fees, and all fees remain subject to Government Code Section 66324 and the Mitigation Fee Act.

Second, any ADU built within existing space, such as a garage or basement conversion, and any ADU under 750 square feet regardless of type, is fully exempt from fees under this subsection. Third, unless the ADU is built together with a new single-family dwelling, the code specifies it is not treated as a 'new' residential use for calculating connection fees, sewer facilities fees or capacity charges, meaning those charges apply only to the extent they already apply to the existing use on the lot, not as if the ADU were a brand-new hookup. 320(4)(A), the fee waiver is a direct financial incentive layered on top of the ministerial permit process to encourage smaller, income-producing units.