Seattle does not charge transportation, school, or park impact fees on ADUs because the city has not adopted general impact fees under RCW 82.02. Permit fees, sewer/water capacity charges from Seattle Public Utilities, and Mandatory Housing Affordability (MHA) fees may apply to larger projects, but standalone ADUs are largely exempt.
Unlike many Washington jurisdictions, Seattle has not adopted school, transportation, or park impact fees authorized by RCW 82.02.050. Therefore standard ADUs pay only SDCI permit fees (typically $3,000-$8,000 for plan review, building, mechanical, electrical, and plumbing combined), SPU water/sewer capacity charges (capped on small infill projects), and a King County wastewater capacity charge collected with the building permit. Mandatory Housing Affordability (MHA) under SMC 23.58B does not apply to single-family or duplex/triplex residential development including ADUs. State law (RCW 36.70A.681, enacted with HB 1337) prohibits owner-occupancy and limits design review for ADUs, and caps any impact fees Seattle might adopt in the future at 50% of those imposed on single-family detached homes for ADUs over 1,000 sq ft and prohibits them entirely for ADUs under 1,000 sq ft.
Failure to pay required SPU and King County capacity charges blocks permit issuance and final inspection. Unpaid fees become a lien on the property and accrue interest. Misrepresenting ADU size to qualify for fee reductions violates SMC 23.90 with civil penalties up to $1,000 per occurrence.
Seattle, WA
Seattle's Land Use Code allows residential lawn ornaments, statuary, and yard art without permits provided structures do not exceed accessory-structure heigh...
Seattle, WA
Seattle does not regulate residential inflatable holiday decorations by size or type. Standard Noise Ordinance (SMC 25.08) limits apply to blower-motor noise...
Seattle, WA
Seattle has no ordinance restricting when residents may put up or take down holiday lights. The general Noise Ordinance SMC 25.08 applies to any amplified ou...
Seattle, WA
Built-in outdoor kitchens in Seattle require building permits from SDCI when they include new electrical, plumbing, gas piping, or a structural roof under Se...
Seattle, WA
Backyard wood and pellet smokers in Seattle are allowed at single-family homes but are subject to Puget Sound Clean Air Agency (PSCAA) Regulation I, Section ...
Seattle, WA
Seattle Fire Code Section 308.1.4 prohibits open-flame cooking devices and LP-gas containers larger than 1 lb on combustible balconies of multi-family buildi...
See how Seattle's adu impact fees rules stack up against other locations.
Help us keep this page accurate. If you notice an error or outdated information, let us know.