How long does an ADU permit take in Seattle?

Typically about 16 weeks from complete application to approval. Seattle SDCI processes DADU permits in $8K–$15K range (New Image 2025). Impact fees for transportation/utilities add several thousand more. Middle housing legislation and DADU rules expanded recently — check current limits before applying.

How much does an ADU permit cost in Seattle?

All-in permit-related costs typically run $8,000–$15,000 (Andalusia Drafting 2026; Dynamic Quality Builders 2026). This includes building permit fees, plan check, and professional soft costs. Impact fees may apply for ADUs over 750 sq ft.

Do I need to replace parking when building an ADU in Seattle?

No — California state law eliminates parking-replacement requirements for ADUs within half a mile of public transit, in historic districts, in existing structures (garage conversions), or where on-street parking permits aren't required. Most Seattle ADUs qualify for at least one of these exemptions.

ADU permits · Seattle, Washington

Seattle ADU permit fees, timeline, and rules

Sourced permit fee ranges, typical approval timelines, and the ADU-specific rules that apply in Seattle. All numbers cross-referenced against published builder data and the city's planning department.

Last validated by OwnAdu: May 15, 2026 (manually verified)

Typical permit fees (all-in)

$8,000 – $15,000

Typical approval timeline

~16 weeks

Maximum ADU size

1,000 sq ft

Parking replacement required

No — exempt under state law in most cases

Owner-occupancy required

Setback requirements

Varies by zone; typically 5 ft side and rear

Source: https://www.seattle.gov/sdci/permits/permits-we-issue-(a-z)/accessory-dwelling-units

Buying a home with an ADU in Washington?

State law, typical premium, what to verify on a permitted ADU, and what to do if you find an unpermitted one.

Washingtonbuyer's guide →

Get a real quote for your Seattle project

Run the cost calculator with Seattle selected to see how local permit fees and timelines affect your all-in budget, or get matched with builders who specialize in Seattle ADUs.

Open the cost calculator See builders in Seattle

Related resources

Get sourced ADU permit updates monthly

Permit fees and timelines change. We re-validate against the source URL above each quarter.