National City, CA Accessory Structures: ADU Impact Fees (2026)

Impact fees for an accessory dwelling unit in National City are set by subsection G.7 of Section 18.30.380 in the Land Use Code (Title 18), and the rule turns on size. An ADU with less than 750 square feet is exempt from any impact fees imposed by the city. An ADU of 750 square feet or more is charged impact fees proportionately in relation to the square footage of the primary dwelling unit. The section prints no dollar amounts and no fee table, so the code text fixes the method, proportion to the primary dwelling, and leaves the underlying fee amounts to the city's fee schedules outside this section.

The 750 square foot line sits inside a wider range of permitted sizes. The smallest ADU the code allows is 150 square feet. A detached ADU is capped at 1,200 square feet. An attached ADU is capped at 50 percent of the existing primary dwelling's floor area or 1,200 square feet, whichever is greater, and a unit built within the footprint of an existing dwelling or detached structure carries no maximum floor area at all. The exemption therefore covers the smaller end of what the code allows, and the proportional charge applies as size climbs toward those caps.

The fee sentence sits with the other limitations in subsection G, next to the requirement that the record owner sign an agreement in a form approved by the City Attorney before a building permit issues. The agreement is recorded by the County Recorder and runs with the land for the life of the ADU. Review is ministerial under Section 18.12.030, and staff act on the building permit application within 60 days after a complete application is received.

Subsection B of the same section adds that if the section is inconsistent with Government Code Section 65852.2, state law prevails. Junior ADUs are handled in Section 18.30.390, which caps them at 500 square feet and prints no comparable fee sentence.