King County • Permissiveness Score: 97/100
Seattle, WA ADU Zoning Rules & Regulations
Seattle allows up to TWO ADUs on any residential lot (one attached AADU + one detached DADU, or two DADUs). Seattle has eliminated all off-street parking mandates and owner occupancy requirements.
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Key Zoning Parameters for Seattle
Verified 2026 Max Detached Size 1,000 sq ft
Max Attached Size 1000
Rear & Side Setbacks 5 ft rear / 5 ft side
Front Setback 20 feet or matching block pattern
Max Height Limit 24 feet (2 stories)
Owner Occupancy Not Required (Waived) Seattle removed owner-occupancy requirements in 2019.
Parking Requirements Exempt No parking required for any ADU in Seattle.
Junior ADU (JADU) Allowed up to 1000 sq ft within primary residence
Short Term Rentals (Airbnb) Allowed with permit Allowed under Seattle Short-Term Rental License limits (max 2 units per host).
Estimated Permit Fees $2,500 - $5,500
Avg Review Timeline 3 - 6 weeks for pre-approved DADUs
Fire Sprinklers Only if city water flow or setback clearance dictates.
Governing Ordinances & State Laws
- ✓ Seattle Land Use Code SMC 23.44.041
- ✓ Washington State HB 1337
Seattle ADU Frequently Asked Questions
Can I build two detached ADUs on my Seattle lot?
Yes! Under updated Seattle land use codes and WA HB 1337, lots may have two secondary units (e.g. 2 detached DADUs or 1 attached and 1 detached).
Does Seattle have pre-approved DADU plans (ADUniverse)?
Yes, Seattle offers the "ADUniverse" program featuring dozens of architect-designed, pre-approved DADU designs that cut permitting time by 75%.
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Top Builders in Seattle
Verified Emerald City Backyard Cottages ★ 4.9
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