Shoreline, WA Accessory Structures: ADU Impact Fees (2026)

Under Shoreline Municipal Code § FEE.030, the city's 2026 park impact fee rate table sets flat per-dwelling-unit charges for new houses: $2,507 for units under 500 square feet, $4,460 for 500 to 1,499 square feet, $6,412 for 1,500 to 2,499 square feet, and $6,940 for 2,500 square feet or more. A separate line item in that same rate table addresses accessory dwelling units directly: the ADU impact fee is "50% of the park impact fee that would be charged to the principal unit on the lot or the rate by square footage of the ADU, whichever is less." In practice that means Planning and Community Development calculates the fee two ways when a permit is filed: half of the principal unit's tier-based fee, and the ADU's own square-footage tier fee, then bills whichever number is smaller.

The same 50%-of-principal-unit approach also governs Shoreline's separate transportation impact fee under § FEE.020, where ITE codes ending in "ADU" (210ADU, 220ADU, 221ADU, 222ADU) are billed at exactly half the per-dwelling-unit rate charged to the matching principal-unit ITE code, a structure the code's own notes tie to RCW 36.70A.681(1)(a) capping ADU impact fees at 50% of the principal unit's fee. Administrative fees for processing are billed separately per § FEE.030(B), referred to Planning and Community Development's own fee schedule. Additions and remodels that add finished square footage are billed the calculated difference between the pre- and post-addition rate tiers rather than a flat fee.