Pierce County, WA Accessory Structures: ADU Impact Fees (2026)

The county's Title 4A impact fee schedule sets traffic impact fees by land use code, with detached single-family homes billed under LUC 210 and ADUs carrying their own line item on the same Table 4-2 schedule. 030, Impact Fee Schedule, states plainly that fees for ADU construction may not exceed half of what the principal unit pays, a discount applied automatically at building permit issuance by the Planning and Public Works Department rather than through a separate application. 30 (School Impact Fees) apply the same 50 percent ADU reduction principle to their own schedules, so a homeowner adding a detached or attached ADU sees the discount carried across every applicable impact fee category, not just traffic.

Rates are indexed to the Institute of Transportation Engineers Trip Generation manual and updated administratively by the County Council; the current schedule reflects the update effective February 1, 2026 under Ord. 2025-516s. Applicants pay these fees at the time of building permit issuance for the new ADU, and the county calculates the discount off whatever base rate applies to the Transportation Service Area (TSA) where the parcel sits, since Pierce County charges different per-trip rates across its TSAs.