A backyard cottage — officially a Detached Accessory Dwelling Unit (DADU) in Seattle — is a freestanding residential building on the same lot as your primary home. Here is everything you need to know to plan, design, permit, and build one in 2026.
What Is a Seattle Backyard Cottage?
A DADU is a completely self-contained home — kitchen, bathroom, sleeping area — that sits in your backyard. It can be used as a rental unit, a multigenerational living space, a home office, or a guest house. In Seattle, you can also rent both your primary home and your DADU simultaneously — no owner-occupancy required since 2019.
Seattle DADU Size and Design Options
- Maximum size: 1,000 sq ft or 60% of primary home floor area, whichever is greater
- Maximum height: 24 ft (pitched roof) or 18 ft (flat roof)
- Studio layouts (300-450 sq ft): Most affordable, fastest to permit and build
- 1-bedroom layouts (500-700 sq ft): Best balance of cost and rental income
- 2-bedroom layouts (750-1,000 sq ft): Maximum rental income, highest construction cost
Seattle DADU Permit Process (2026)
- Lot feasibility check: zoning, setbacks, coverage (2-4 weeks with architect)
- Design development: floor plans, elevations, structural approach (6-10 weeks)
- Construction documents: permit-ready drawing set (4-8 weeks)
- SDCI permit review: 8-14 weeks standard; allow for one correction cycle
- Permit issuance: 1-2 weeks after approval
- Construction: 6-12 months
Seattle DADU Construction Costs (2026)
- Studio DADU (350 sq ft): $150,000-$230,000
- 1-bedroom DADU (600 sq ft): $250,000-$380,000
- 2-bedroom DADU (900 sq ft): $360,000-$480,000
- Architect fees: $18,000-$38,000
DADU Rental Income in Seattle (2026)
- Studio: $1,400-$1,900/month
- 1-bedroom: $1,800-$2,500/month
- 2-bedroom: $2,400-$3,200/month
Ready to start? See our ADU service or get a free consultation — call 425-753-6452.