Not every backyard structure requires a building permit in Seattle, but many do. Here is a guide to when permits are required for accessory structures.
Exempt Structures (No Permit Required)
- Detached accessory structures under 200 sq ft floor area AND not exceeding 15 feet in height AND not used for human habitation AND not located in a flood zone or critical area
- Simple patios, walkways, driveways at grade
- Fences under 8 feet tall (except in shoreline areas)
Permit Required
- Any structure over 200 sq ft
- Any structure exceeding 15 feet in height
- Garages (attached or detached), regardless of size
- Carports over 200 sq ft
- Any structure used for habitation (ADU, studio, office)
- Structures in flood zones or critical areas
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.
Setback Requirements for Accessory Structures
In most Seattle residential zones, accessory structures must be:
- 5 feet from rear lot line
- 5 feet from side lot lines
- Behind the primary structure or at least 20 feet from front lot line
When a Permit Is Required: What It Involves
Permitted accessory structures require a site plan, floor plan, elevation drawings, and energy compliance documentation if heated. Structural drawings are required for any structure with a concrete foundation or more than basic wood framing.
Piper Cole Architects designs and permits accessory structures of all types. 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:
