Updated January 2026 | Seattle DADU regulations current as of ordinance update effective July 2024
Seattle DADU Rules (2025-2026)
Seattle legalized Detached Accessory Dwelling Units (DADUs) citywide in 2019, then expanded the rules in 2024. Here is what you can actually build:
- Maximum size: 1,000 sqft or 50% of lot size, whichever is less
- Height limit: 24 feet in most zones, 22 feet in lowrise zones
- Setbacks: 5 feet from side/rear property lines (reduced from previous 8 ft)
- Owner occupancy: NOT required as of 2024 – huge change for investors
- Parking: No additional parking required citywide
Contractor Quote: “I’m building DADUs for $280-$350/sqft right now. A typical 800 sqft unit runs $224,000-$280,000 turnkey. Add $15,000-$25,000 for utility connections if you can’t tap existing service.” – Sarah Okonkwo, Greenwood Construction, December 2025
Actual Permit Costs
- Building permit: $6,500-$9,000
- Plan review: $2,500-$4,000
- Impact fees (SEPA): $3,000-$8,000
- Sewer connection: $5,000-$15,000 (varies by distance)
- Total permit/fee costs: $17,000-$36,000
Rental Income Potential
Current Seattle DADU rents (December 2025 data from Zillow):
- 600 sqft studio: $1,600-$1,900/month
- 800 sqft 1BR: $2,100-$2,500/month
- 1,000 sqft 2BR: $2,600-$3,100/month
At $2,200/month rent, a $270,000 DADU generates ~$26,400/year gross income. After expenses (maintenance, insurance, vacancy), expect ~$18,000-$20,000 net. That is a 7-7.5% return – competitive with other real estate investments.
Neighborhood Considerations
DADU construction is concentrated in neighborhoods with larger lots and alley access:
- Best for DADUs: Ballard, Phinney Ridge, Greenwood, Columbia City, Rainier Beach
- Challenging: Capitol Hill (small lots), Queen Anne (steep terrain), Magnolia (restrictive covenants)
