Bothell, WA Accessory Structures: ADU Impact Fees (2026)
Key Facts
- Cap
- ADU impact fees limited to 50 percent of the principal unit's fees
- Transportation rate, ADU
- $3,311 per dwelling unit (2026 schedule)
- Transportation rate, single-family
- $13,387 per dwelling unit (2026 schedule)
- Fee timing
- Paid when the permit is ready for issuance
- Appeal
- Impact fee amount appealable under BMC 17.045.020
- Frontage improvements
- ADU building permits exempt, BMC 17.09.010(B)(2)(a)
Summary
In the City of Bothell, Washington, BMC 12.14.135(G) bars the city from assessing impact fees on an accessory dwelling unit that are greater than 50 percent of the impact fees imposed on the principal unit. The transportation impact fee schedule in BMC 17.045.070 lists a separate ADU rate.
G. The city will not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on the principal unit.
Full Breakdown
The cap sits in subsection G of the City of Bothell's accessory dwelling unit section, BMC 12.14.135. It says the city will not assess impact fees on the construction of ADUs that are greater than 50 percent of the impact fees that would be imposed on the principal unit. The wording applies to impact fees as a class, so it limits the ADU charge relative to whatever the principal dwelling pays.
The only impact fee schedule printed with rates in the Bothell Municipal Code is the transportation schedule in Chapter 17.045 BMC. BMC 17.045.070 says the schedule is based on the city's 2026 rate study. It lists the cost per new person trip generated at $9,928. Single-family is listed at 1.35 net new person trips per dwelling unit and a rate of $13,387 per dwelling unit. An accessory dwelling unit has its own line at 0.33 person trips per dwelling unit and $3,311 per dwelling unit, with a footnote citing ADU trip rate recommendations from a 2023 Transpo Group memo.
Payment mechanics come from BMC 17.045.007. Developers pay the impact fee when the development permit is ready for issuance, and pay an impact administrative fee at the time of application, set in the fee schedule the city council adopts by resolution. Fees can be paid under protest to obtain a permit. BMC 17.045.020 lets a developer appeal the amount of an impact fee determined by the director under BMC Title 11, with the burden of proof on the developer. Refunds under BMC 17.045.010 go to a developer who does not proceed with the development activity. Separately, BMC 17.09.010(B)(2)(a) exempts building permits for an ADU from frontage improvement requirements, and BMC 12.14.135(F) says the ADU application fee covers the building inspection for units created without approval.
Violations & Fines
The cap protects the applicant, so a violation is a charge above it: a developer who believes the city assessed more than the 50 percent limit can appeal the amount under BMC 17.045.020 and Title 11, and can pay under protest to obtain the permit per BMC 17.045.007(F). Building or occupying an ADU without approval is enforced under Chapter 11.20 BMC, with a civil penalty of up to $250.00 per day.
Frequently Asked Questions
Does the City of Bothell charge full impact fees on an ADU?
What is the Bothell transportation impact fee for an ADU?
When do I pay Bothell impact fees on an ADU?
Can I appeal a Bothell impact fee amount?
Sources & Official References
Other rules in Bothell
Compare Bothell to another location·View the Washington accessory structures overview
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ADU Impact Fees in Nearby Cities
How other cities in King County handle adu impact fees.