Pierce County, WA Environmental Rules: Flood Elevation Requirements (2026)

a sets the county's freeboard standard for single-family, two-family, multi-family, mobile/manufactured, commercial and industrial structures: the lowest floor must be elevated a minimum of 1 foot above base flood elevation with a crawlspace, or a minimum of 2 feet above base flood elevation with slab-on-grade construction, and flood resistant materials and construction methods must be used. b must have the bottom of the lowest horizontal structural member at least 2 feet above base flood elevation, engineered by a professional structural engineer, with the space below kept free of obstructions; fully enclosing that space is prohibited, though screens, louvers and collapsible mobile-home skirting are allowed.

b: 3 feet of freeboard above base flood elevation for slab-on-grade or crawlspace, and the same 3 feet for the lowest horizontal member on piers or pilings, plus armoring and flood-resistant materials. Coastal flood hazard areas carry their own elevated standards: mechanical and electrical equipment must sit 2 feet above base flood elevation, and structures on piers or pilings seaward of that 2-foot line need the lowest structural member 2 feet above base flood elevation. 3, a FEMA elevation certificate is required for new construction, side additions, and substantial improvements in flood hazard areas, prepared by a Washington-licensed professional land surveyor and kept on file with the Planning and Public Works Department; additional certifications apply to V-zone construction, engineered flood openings, and dry floodproofing.