Shoreline, WA Fence Regulations: Retaining Walls (2026)

Shoreline classifies landslide, seismic, and erosion hazard areas under SMC § 20.80.215, and treats slopes already stabilized by an engineered rockery or retaining wall built and approved to its design as exempt from the chapter's alteration provisions, based on a qualified professional's opinion that the structure still performs as designed. If that professional instead determines the rockery or wall is inadequate, SMC § 20.80.215(E) requires the owner to submit a permit for a new or rebuilt wall, which the Department reviews for code compliance before work proceeds.

Where a site sits in a very high risk landslide hazard area (slopes over 40 percent and more than 20 feet high, or slopes with emergent groundwater or active scarps), SMC § 20.80.230(E) sets design criteria requiring a factor of safety of at least 1.5 under static conditions and 1.2 under dynamic or seismic loading, and directs that retaining walls preserving the natural slope be used in preference to graded artificial slopes when native vegetation alone cannot hold the grade. Projects in very high risk areas also trigger SMC § 20.80.230(F): a neighborhood meeting under SMC § 20.30.090, a recorded covenant acknowledging landslide risk and waiving claims against the City, and insurance or bonding from piling and excavation contractors when excavation exceeds four feet below the property's 45-degree slope line. The Building Official may suspend an active permit and demand a geotechnical engineer's written re-certification if site conditions change during construction.