Kennewick, WA Accessory Structures: Shed Rules (2026)

Washington does not preempt local accessory-structure regulation. KMC Title 18 sets accessory-use standards by zoning district. Typical Kennewick residential standards require sheds in the rear yard behind the front building line of the principal dwelling, with side and rear setbacks commonly in the 3- to 5-foot range for accessory structures (district-specific in KMC Chapter 18.12 and the table of district standards), a maximum height for accessory structures (commonly around 15 feet), and aggregate accessory-structure lot coverage caps. Front and street-side setbacks match the principal-building setback for the district. The Washington State Building Code Council adoption of IRC R105.2 at WAC 51-51 typically exempts one-story detached accessory structures of 200 square feet or less from a building permit, provided the structure is not used for habitation, has no electrical or plumbing connections requiring separate permits, and does not exceed a single story. The exemption is from the building permit only — zoning compliance under KMC Title 18 is still required, and Kennewick Planning issues a zoning clearance or accessory-structure permit confirming setbacks and lot coverage. Sheds over 200 square feet require a building permit with structural review under IRC Chapter 8 and the Washington amendments. Climate-Zone 5B (eastern Washington) design loads apply: ground snow load commonly 15 to 25 psf depending on elevation, basic wind speed approximately 100 mph (ASCE 7), and seismic Design Category D1 in the Mid-Columbia.