Mirrormont Accessory Structures: Carport Rules Rules (2026)

A carport in unincorporated King County is regulated as an accessory structure under KCC Title 21A. An attached carport needs a building permit under KCC Title 16 and must meet the side and rear setbacks for the underlying residential zone (commonly 5 feet side and 10 feet rear in R zones, with larger rural setbacks in RA zones). Detached accessory structures under 200 square feet and not attached to a dwelling are typically exempt from building permits under IRC Section R105.2, but they still must comply with setback and critical-area rules. Carports add impervious or partially impervious area; projects that push total new impervious surface over 2,000 square feet may require stormwater review under the King County Surface Water Design Manual. In critical areas such as steep slopes, shoreline setbacks, or wetland buffers, carports are generally prohibited or require variance review. Height typically is capped at 15 feet for one-story accessory structures or the underlying zone limit. Carports must have a Class A or B roof covering in designated wildfire hazard areas per the Wildland Urban Interface Code. HOAs in developments like Sammamish Plateau, Klahanie, and Snoqualmie Ridge often restrict carports, preferring enclosed garages.