ADU Impact Fees: Bellevue vs Seattle
How do adu impact fees rules compare between Bellevue, WA and Seattle, WA?
Bellevue and Seattle have similar restriction levels.
Bellevue, WA
King County
Bellevue exempts ADUs from transportation and school impact fees in practice, consistent with Washington HB 1337 (RCW 36.70A.696), which caps any ADU impact fee at 50 percent of the single-family rate. Only standard plan-review and building-permit fees apply, plus utility connection charges if a new water or sewer service is needed.
View full Bellevue 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 | Bellevue | Seattle |
|---|---|---|
| Transportation Impact Fee | Exempt for ADUs | - |
| School Impact Fee | Exempt for ADUs | - |
| State Cap | 50% of SFR (RCW 36.70A.696) | - |
| Building Permit | Per WA fee schedule | - |
| 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.
Bellevue FAQ
Does Bellevue charge impact fees for ADUs?
No. Bellevue's current practice exempts ADUs from both transportation and school impact fees. Washington RCW 36.70A.696 also caps any ADU impact fee at 50 percent of the single-family rate, so even if the policy changes, fees cannot exceed half of the standard SFR rate.
What fees do I still pay for a Bellevue ADU?
Standard building, plan-review, and trade permit fees scaled to construction valuation. Utility connection fees from Bellevue Utilities only apply if you add a new water or sewer service line. Stormwater fees apply if new impervious surface exceeds the BCC threshold.
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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