ADU
In Practice
When budgeting for an ADU project, impact fees are a distinct cost category separate from building permit and plan check fees. In jurisdictions where state law has enacted impact fee waivers for ADUs, the savings can be substantial. In cities where impact fees apply without such a waiver, they can add meaningfully to the total cost of an ADU permit. Always verify the specific impact fee obligations for your city and ADU type early in the planning process — these fees are not always prominently disclosed on general ADU information pages.
Source: How Much Does It Cost to Build an ADU? (By City) · Verified April 5, 2026