When lot coverage is limited but you want a larger ADU, building up rather than out is often the answer. A two-story detached ADU can deliver 800 to 1,000 sq ft on a small ground footprint. Here is how.
Why Build a Two-Story ADU
Seattle limits DADU floor area to 1,000 sq ft and limits lot coverage. A two-story design lets you reach the maximum floor area while minimizing the ground footprint, preserving yard space and meeting lot coverage limits.
Height Limits
Seattle allows DADUs up to 24 feet with a pitched roof (or 18 feet flat). This comfortably accommodates two stories. The first floor typically holds living, kitchen, and a bathroom; the second floor holds a bedroom and second bathroom.
Planning a project?
Wondering what an ADU on your lot would cost?
Send David the address and a few lines about what you want. The first feasibility check is free and usually takes about a day: what the site and the code are likely to allow, and what to check first.
Architect since 1996, member of the AIA and NCARB. Three Masonry Excellence Awards for commercial projects; the Carr residence was featured in Above The Lake and Lux magazines.
Design Strategies
- Place the living space and kitchen on the ground floor for accessibility
- Use the upper floor for bedrooms to maximize privacy
- Add a small deck or roof terrace where setbacks allow
- Large windows on the upper floor capture light and views above fence height
Cost (2026)
- Two-story DADU (800 to 1,000 sq ft): $300,000 to $480,000
- Architect fees: $25,000 to $40,000
Rental Income Potential
A two-bedroom two-story ADU commands premium rent in Seattle, $2,400 to $3,200 per month. See our ADU rental income analysis and ADU design service.
Authoritative sources
Regulatory requirements referenced in this guide are set by the official agencies below. Rules change, always confirm current requirements with the source:
