Bellevue, WA has updated its ADU regulations in alignment with Washington State law. Here is a current guide to what homeowners in Bellevue can build in 2026.
ADU Types Allowed in Bellevue
- Detached ADU (DADU): Freestanding backyard structure on the same lot as the primary home
- Attached ADU: Internal conversion or addition — basement, garage conversion, or added suite
- Bellevue allows both types per lot in residential zones
Bellevue ADU Size and Height Limits (2026)
- Maximum DADU size: 1,000 sq ft
- Maximum height: 24 ft (sloped roof) or 18 ft (flat roof) in most zones
- Setbacks: 5 ft rear and side in most residential zones
Bellevue vs. Seattle ADU Rules
Bellevue generally has faster permit review (4-8 weeks vs. Seattle’s 8-14 weeks). Bellevue’s lot coverage limits and setback requirements are similar to Seattle but may vary by zone. Bellevue’s development services team is known for more predictable review timelines.
Free Consultation for Bellevue ADU Projects
Piper Cole Architects has permitted multiple ADUs in Bellevue. See our ADU service or contact us for a free consultation. Call 425-753-6452.
Ready to Start Your Project?
Piper Cole Architects offers a free initial consultation for all project types — residential, commercial, ADU, and renovation. No obligation. Based in Kirkland, WA. Serving the entire Seattle metro area since 2000.