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
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 consultation — call 425-753-6452.
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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.