Seattle, WA · Updated 2026
Seattle ADU Permits: Fees, Timeline & Process
Two ADUs per lot, no owner-occupancy, and pre-approved DADU plans under HB 1337.
Quick Answer
Seattle ADUs: $400K–$600K
Permits: $20K–$40K · Updated April 2026
Seattle ADU Permitting: Overview
Seattle is one of Washington's most active ADU markets, driven by House Bill 1337 which requires all cities to allow two ADUs per lot and prohibits owner-occupancy requirements. The city permits both Attached ADUs (AADUs) and Detached ADUs (DADUs) through the Seattle Department of Construction and Inspections (SDCI).
Seattle's 2025 permit fee increases averaged 12%, with some larger projects seeing 19% hikes. The city offers pre-approved DADU plans that streamline the review process. Under the new Urban Residential (UR) zoning code, the allowable Floor Area Ratio increased from 0.9 to 1.2, giving more design flexibility for ADUs.
Permit Fees Breakdown
Total permitting costs in Seattle typically range from $20,000–$40,000 depending on ADU type, size, and site conditions.
| Fee Type | Amount | Notes |
|---|---|---|
| Base Permit Fee | $2,800–$8,000 | Based on square footage and complexity |
| Plan Review | $2,000–$4,000 | May be included in base permit |
| Utility Connection (Water) | $5,000–$15,000 | New water service connection |
| Sewer Capacity Charge | $3,000–$8,000 | Varies by district |
| Electrical Service | $2,000–$5,000 | Panel upgrade or new service |
| Energy Code Compliance | $500–$1,500 | Title compliance review |
| Impact Fees (Transportation) | $2,000–$5,000 | Where applicable |
| Inspection Fees | Included | Part of building permit fee |
Fees are estimates based on typical ADU projects. Contact Seattle permitting for exact quotes. See our full permit fees guide for comparison across cities.
Zoning & Requirements
- DADUs and AADUs allowed in all Neighborhood Residential (NR) and Urban Residential (UR) zones
- Two ADUs per lot permitted (one attached + one detached)
- No minimum lot size requirement
- DADU max size: 1,000 sq ft (or larger under UR zoning)
- Height limit: 22–25 feet depending on roof type
- Setbacks: 5 feet rear/side for DADUs
- No parking required for ADUs
- No owner-occupancy requirement (HB 1337)
- FAR increased to 1.2 under new UR zoning
Step-by-Step Permit Process
Verify zoning eligibility
Use Seattle's interactive zoning map to confirm your lot is in an NR or UR zone and check setback requirements.
Prepare construction documents
Full set of construction drawings, site plans, floor plans, and elevation views. Consider pre-approved DADU plans for faster review.
Submit to SDCI
Apply online through the Seattle Services Portal. Upload all required documents and pay initial fees.
Plan review (3–6 months)
Building, zoning, and fire departments review plans. Seattle has high application volumes — expect longer review times than smaller cities.
Address corrections
Respond to any plan check comments. Multiple revision cycles are common for custom designs.
Permit issuance
Pay remaining fees. The permit is valid for 18 months with options to extend.
Construction & inspections
SDCI inspectors check foundation, framing, mechanical systems, and final completion.
Certificate of Occupancy
Pass final inspection to receive CO. Both the main house and DADU can then be rented.
Key Regulations & Laws
Washington HB 1337 (2023)
Requires all cities to allow two ADUs per lot, eliminates owner-occupancy requirements, and prohibits parking mandates near transit.
Urban Residential (UR) Zoning
Seattle's 2024 zoning update increased FAR from 0.9 to 1.2 and expanded flexibility for multi-unit development on single-family lots.
Pre-Approved Plans
Seattle offers pre-approved DADU designs that reduce plan review time and avoid revision cycles.
2025 Fee Increases
Seattle construction permit fees increased an average of 12% in 2025, with larger projects seeing up to 19% increases.
Frequently Asked Questions
How much do ADU permits cost in Seattle?
Permits typically range from $8,000–$15,000 for the building permit alone. Including utility connections and impact fees, total permitting costs run $20,000–$40,000. Seattle's 2025 fee increases added 12–19% to many project costs.
How long does it take to get an ADU permit in Seattle?
Plan review typically takes 3–6 months due to high application volumes. Pre-approved plans can reduce this. The full project from design to completion runs 12–18 months for custom builds.
Can I build two ADUs on my property in Seattle?
Yes. Under HB 1337, you can build both an attached ADU (AADU) and a detached ADU (DADU) on the same single-family lot.
Do I need to live on the property to build a DADU?
No. Washington's HB 1337 eliminated owner-occupancy requirements statewide. You can rent out both the main house and any ADUs.
Your Next Steps
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