What's the total ADU permit fee in Seattle?

Total Seattle ADU permit fees in 2026 run roughly $5,500–$14,000 depending on size, type, and any utility hookups required.

How long does Seattle ADU permit review take?

Standard Seattle ADU plan review takes 6–16 weeks. Pre-approved plans and complete submittals can shorten that significantly.

What fees are NOT included in the base Seattle permit cost?

Utility connection fees (water, sewer, electric), school impact fees, drainage and fire-line upgrades, and any private-engineering studies typically add 30–60% to the base permit number.

Can I get my Seattle ADU permit fees reduced or waived?

Some jurisdictions offer fee reductions for deed-restricted affordable ADUs, JADUs under 500 sq ft, or projects using pre-approved plans. Check Seattle's current ADU ordinance for available waivers.

ADUCosts

Seattle, WA

Seattle ADU Permit Fee Calculator (2026)

Name: aduglossary.com — Seattle WA ADU Resources
Price range: $

Instant fee breakdown for Seattle, Washington. Total range: $5,500–$14,000.

Seattle, Washington ADU Permit Fees

Total estimated range: $5,500–$14,000

Plan Check

$1,000–$2,500

Building Permit

$2,000–$4,500

Impact Fees

$0–$8,000

School Fees

N/A

Utility Hookups

$2,500–$7,000

Source: City permitting schedules and FeeBuilder surveys, updated April 2026.

Seattle permit process at a glance

Permitting office: Seattle Department of Construction and Inspections (SDCI)

Typical plan review: 14-22 weeks

Seattle removed the owner-occupancy requirement for DADUs in 2019, and the city now allows up to two ADUs per lot (one attached, one detached). SDCI's pre-approved DADU catalog has grown to about 20 designs that cut plan review to 6-8 weeks if you build straight from the catalog. The Pacific Northwest rain climate is the dominant cost driver — moisture detailing, rain screens, and code-mandated whole-house ventilation per the Washington Energy Code each add real dollars.

Sample real-world fee example

Scenario: 700 sq ft detached ADU on a typical Seattle lot

Plan check (mid)	$1,200
Building permit (mid)	$2,300
Utility connection (low end)	$2,500
Misc fees (records, inspections)	$1,500
TOTAL (rough mid example)	~$7,000

Common Seattle ADU permit mistakes

Skipping the SDCI pre-approved DADU catalog check — catalog submittals can cut review to 6-8 weeks.
Missing the Washington Energy Code whole-house mechanical ventilation requirement.
Not checking Environmentally Critical Areas overlay (steep slopes, peat bogs, riparian).
Forgetting that Seattle now allows two ADUs per lot — many homeowners over-design the first when they could split into two smaller units.

How Seattle compares nearby

City	Total fee range	Link
Seattle	$5,500–$14,000	(this page)
Portland	$4,300–$11,500	View →
Denver	$6,300–$11,500	View →

Full Seattle cost guide ROI calculator Compare all 18 cities

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