Mercer Island ground, weather, and permits
Mercer Island’s ground changes from hillside to hillside. A geotechnical report on West Mercer Way places its lot near the contact between Vashon advance outwash, a permeable sand with gravel, and Lawton Clay, a stiff silt and clay that can hold light groundwater. A report for another island lot describes glacial till, with seepage possible where it meets unweathered till. The city’s infiltration feasibility map also marks areas where infiltrating drainage is not permitted. Which soil, slope, and map layer sit under your lot is a parcel question.
Community Planning and Development issues building permits, and Real Property Services issues street occupancy permits for right-of-way work. On lots mapped as erosion, potential slide, or steep slope hazards, land clearing, grading, filling, and foundation work are not permitted from October 1 to April 1 unless the city grants a waiver. Lot coverage is capped by slope, from 40 percent on gentle lots to 20 percent above a 50 percent slope. Before pricing, we look up your parcel’s hazard mapping and coverage limit.
Nearby, we also build in Newcastle, Renton, West Seattle, Issaquah, and Tukwila, and we serve the rest of Pierce and South King County.