How Seattle Handles Accessory Structures: A Practical Guide
Seattle maintains 177 local ordinances across all categories, and 2 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Seattle falls on the strict-to-permissive spectrum compared to other cities.
Tiny Homes
Seattle allows tiny houses on permanent foundations as Detached Accessory Dwelling Units (DADUs) under SMC 23.42.022 and SMC 23.44.041, subject to the same code as any DADU. Tiny houses on wheels (THOWs) are treated as recreational vehicles and may not be used as residences in city residential zones. Sanctioned tiny house villages exist only as transitional encampments under SMC 23.42.054.
Key details: Code Section: SMC 23.42.022, 23.44.041. Foundation: Permanent required (no THOWs). Max Size as DADU: 1,000 sq ft. Max Height: 32 ft (NR/RSL zones). Village Code: SMC 23.42.054.
Living in a tiny house on wheels in a Seattle residential zone is treated as illegal occupancy of an RV/vehicle and is subject to removal and SDCI notice of violation. Unpermitted tiny-house DADU construction triggers a stop-work order and penalties. Transitional encampments operating outside SMC 23.42.054 standards are subject to permit revocation and shutdown.
Shed & Carport Rules
SMC 23.44.090(G) lets garages and carports sit in a required setback under specific conditions: a front-setback garage is capped at 300 square feet and 14 feet wide for one space, or 600 square feet and 24 feet wide for two, and a rear-setback garage must stay 5 feet off the rear line.
Key details: Front-setback garage cap (1 space): 300 sq ft, 14-ft width. Front-setback garage cap (2 spaces): 600 sq ft, 24-ft width. Rear setback minimum: 5 feet from rear property line. Side setback option: Recorded neighbor agreement or alley/rear proximity. Governing section: SMC 23.44.090(G).
Building a garage or carport larger than the 300-square-foot/14-foot (one space) or 600-square-foot/24-foot (two space) front-setback cap, placing it closer than 5 feet to a rear lot line, or locating it in a side setback without the recorded neighbor agreement required by SMC 23.44.090(G)(2)(b) is a zoning violation; SDCI will require the structure to be resized, relocated, or brought into full Table A setback compliance.
The Bottom Line
Seattle's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Seattle is broadly strict or permissive.
Keep in mind that Seattle can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.