Kirkland, WA Accessory Structures: ADU Impact Fees (2026)
Key Facts
- ADU fee cap
- 50% of principal-unit impact fee
- Small-ADU exemption
- 800 sq ft or less pays no fee
- Deferral admin fee
- $240 per building permit
- Independent fee study fee
- $100 per calculation
- Deferral deadline
- 18 months after permit issuance
- Administering department
- Kirkland Public Works Department
Summary
Kirkland caps the transportation impact fee on a new accessory dwelling unit at fifty percent of the fee that would apply to the principal house on the same lot. The cap, set by KMC 27.04.030(m) to comply with the state ADU statute, applies once an ADU exceeds 800 square feet, the point where the city's separate small-ADU exemption stops covering it.
To ensure compliance with RCW 36.70A.681(1)(a), the impact fee assessed on the construction of an accessory dwelling unit regulated in Chapter 115 KZC will not be greater than fifty percent of the impact fee that would be imposed on the principal unit.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 4945, passed July 21, 2026).
Full Breakdown
The Public Works Department collects transportation impact fees from every applicant for a building permit, using the land use category and rate schedule in KMC 27.04.150, and it decides which category an ADU falls into under 27.04.030(a). Fees are due before the building permit is issued (27.04.030(b), (h)), but under 27.04.030(m) the fee on an ADU regulated by KZC Chapter 115 cannot exceed fifty percent of the fee charged for the principal unit, a cap the city adopted specifically to track RCW 36.70A.681(1)(a). A smaller carve-out sits in the exemptions section: any legal ADU of 800 square feet or fewer is treated as part of the single-family use and pays no transportation impact fee at all under 27.04.050(a)(1); the 50 percent cap is what governs ADUs larger than that threshold.
Applicants who think the standard schedule overstates an ADU's traffic impact can request an independent fee calculation from a traffic engineer under 27.04.040, paying a $100 administrative processing fee, and the director may set an alternative fee based on that study. Owners of single-family or attached residential permits, ADUs included, may also elect to defer payment until the permit is completed or eighteen months after issuance, whichever comes first, by paying a $240 administration fee under 27.04.030(g); the deferred fee is then due before final inspection, final occupancy, or the eighteen-month deadline. Director decisions on independent fee calculations can be appealed to the hearing examiner under the procedure in 27.04.130.
Violations & Fines
No building permit for an ADU is issued until the capped or exempted fee is paid in full, per KMC 27.04.030(h); permits placed on the deferred-payment track must have the outstanding fee, less credits, paid before final inspection, final occupancy, or eighteen months after issuance, whichever is first. Missing the deferred deadline stops final inspection and occupancy sign-off. Applicants using the deferral option owe a nonrefundable $240 administration fee regardless of when the underlying impact fee is ultimately paid.
Frequently Asked Questions
Does Kirkland cap transportation impact fees for ADUs?
Is my small backyard ADU exempt from impact fees entirely?
Can I delay paying the ADU impact fee?
What if I think the standard fee overstates my ADU's traffic impact?
Sources & Official References
Other rules in Kirkland
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ADU Impact Fees in Nearby Cities
How other cities in King County handle adu impact fees.