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.
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.
Ready to Start Your Project?
Piper Cole Architects offers a free initial consultation for all project types. Based in Kirkland, WA. Serving the entire Seattle metro area since 2000.