Mirrormont Building Setbacks & Zoning: Structure Height Limits Rules (2026)

King County Code Title 21A Chapter 21A.12 sets maximum structure heights by zoning district. Standard single-family residential zones (R-1 through R-8) cap primary structures at 35 feet measured from the average building elevation to the highest point of the roof. Accessory structures including detached garages, sheds, and accessory dwelling units are limited to 25 feet, or not to exceed the height of the primary dwelling where that is less. Rural Area and Agricultural zones allow up to 45 feet for barns and agricultural outbuildings. Commercial and mixed-use zones range from 35 to 80 feet with bonus height available for affordable housing or transit-oriented development. Height is measured differently on sloping lots — average building elevation is calculated from grade at each corner of the building. Chimneys, antennas, church steeples, flagpoles, and mechanical equipment may exceed height limits by a limited amount. Areas near the Boeing Field / King County International Airport and Sea-Tac Airport are subject to additional FAA Part 77 imaginary surface restrictions and Airport Compatibility Review. Shoreline jurisdiction under the Shoreline Master Program further limits building height to protect views and shoreline character, often restricting structures to 30 feet or 35 feet depending on the shoreline designation.