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 ADU size: 1,200 sq ft (LUC 20.20.120), with some parking and unheated storage exempt
- Maximum height for a detached ADU: 24 ft, or 28 ft when built over an existing accessory structure
- Setbacks: a detached ADU follows the middle housing setbacks, 5 ft side and 10 or 15 ft rear depending on the zone, set out in the Bellevue zoning guide
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.
Bellevue vs. Seattle ADU Rules
Bellevue generally has faster permit review (6-10 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 Feasibility Check for Bellevue ADU Projects
Piper Cole Architects has permitted multiple ADUs in Bellevue. See our ADU service or contact us for a free feasibility check. Call 425-753-6452.
Authoritative sources
Regulatory requirements referenced in this guide are set by the official agencies below. Rules change, always confirm current requirements with the source:
