ADU Impact Fees: Kent vs Seattle
How do adu impact fees rules compare between Kent, WA and Seattle, WA?
Kent and Seattle have similar restriction levels.
Kent, WA
King County
Kent waives Park and Transportation Impact Fees for the first ADU on a single-family lot and reduces them by 50 percent for the second ADU under KCC 15.08.250, consistent with Washington's RCW 36.70A.696 cap. Applicants still pay building, plan-review, and trade permit fees, plus utility connection charges only if a new service line is required.
View full Kent rules →Seattle, WA
King County
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.
View full Seattle rules →Key Facts Comparison
| Fact | Kent | Seattle |
|---|---|---|
| State Cap | 50% of SFR (RCW 36.70A.696) | - |
| Park/Transportation 1st ADU | Waived | - |
| Park/Transportation 2nd ADU | 50% of SFR | - |
| School Impact Fee | Kent SD rate applies | - |
| Electrical Permit | WA L&I (not city) | - |
| Utility Connection | Only if new service | - |
| City Impact Fees | - | None (school/parks/transportation) |
| MHA Fee | - | Not applicable to ADUs |
| Permit Fees | - | ~$3-8K typical |
| SPU Capacity Charge | - | Yes, capped for infill |
| Future Fee Cap | - | RCW 36.70A.681 |
Highlighted rows indicate differences between cities.
Kent FAQ
Does Kent charge impact fees on ADUs?
Park and Transportation Impact Fees are waived for the first ADU on a Kent lot and reduced to 50 percent of the single-family rate for the second ADU under KCC 15.08.250 and Washington RCW 36.70A.696. School impact fees for the Kent School District still apply at the standard rate.
What fees do I still owe for a Kent ADU?
Building permit (scaled to construction valuation), plan review, plumbing, gas, and mechanical permits through MyBuildingPermit.com, plus an electrical permit from Washington L&I. Water meter or side-sewer connection fees apply only if you add a new service. Stormwater fees apply if new impervious surface exceeds the threshold in KCC Title 7.
Seattle FAQ
Does Seattle charge impact fees on ADUs?
No. Seattle has not adopted transportation, school, or park impact fees under RCW 82.02. ADU costs are limited to SDCI permit fees plus SPU and King County wastewater capacity charges.
Does MHA (Mandatory Housing Affordability) apply to my ADU?
No. MHA under SMC 23.58B applies only to commercial, multifamily, and certain redevelopment projects. Single-family additions, AADUs, and DADUs are excluded.
What about water and sewer hookup charges?
SPU charges a Water System Development Charge and Capacity Charge; King County collects a Capacity Charge for regional wastewater. For ADUs on the same lot as an existing dwelling, the charges are reduced when capacity is already in place.
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