Sussex County, DE Environmental Rules: Flood Elevation Requirements (2026)

Under Section 115-141.5B(1)(a), the lowest floor, including any basement, of a residential structure or the residential portion of a mixed-use structure in Zones A, AE or AO must be elevated to or above the base flood elevation shown on the county's Flood Insurance Rate Map. Nonresidential structures face the same floor elevation standard under Section 115-141.5C(1)(a), or the building may instead be dry floodproofed watertight to the base flood elevation and certified by a Delaware-registered professional engineer or architect per Section 115-141.5C(2). In Zone AO shallow-flooding areas, Section 115-141.5B(1)(b) requires the lowest floor to sit at least as high above the highest adjacent grade as the depth number printed on the flood map, or at least two feet if no depth number is shown.

The code defines freeboard at Section 115-141.2 as a safety margin expressed in feet above the flood elevation, but Article XVIII does not make freeboard mandatory for the base elevation requirement itself; instead, Section 115-141.10 gives builders an incentive: permitted building height in a special flood hazard area is measured from the base flood elevation, and that height may be increased by one foot for every foot of freeboard added, capped at a two-foot bonus. Manufactured homes must be set on a permanent, reinforced foundation raising the lowest floor to or above the base flood elevation per Section 115-141.5B(3)(a)[1].

Enclosures below the lowest floor used for parking, access or storage must carry flood openings with a net area of at least one square inch per square foot of enclosed area, per Section 115-141.5B(2)(c)[2]. Elevation certificates documenting finished construction elevations must be submitted to the Floodplain Administrator before a certificate of occupancy issues, under Section 115-141.3G(1).