Franklin County, NC Environmental Rules: Flood Elevation Requirements (2026)

Franklin County's flood maps include Zone AO areas, described in § 9.2.2 as shallow flooding areas with base flood depths of roughly 1 to 3 feet, where a defined channel does not exist and the path of flooding is unpredictable. For those areas, § 9.2.5(F) sets an elevation standard distinct from the county's regular Base Flood Elevation-plus-freeboard rule: the reference level of a new or substantially improved structure must be raised at least as high as the depth number shown on the Flood Insurance Rate Map, in feet, plus 4 feet of freeboard, measured above the highest adjacent grade; if the FIRM lists no depth number for the lot, the minimum drops to 2 feet above the highest adjacent grade.

Non-residential structures may be floodproofed to that same elevation instead of physically raised, provided the design keeps the structure and its utilities watertight against hydrostatic and hydrodynamic loads, certified in accordance with § 9.2.5(B)(2). Section 9.2.5(F) also requires adequate drainage paths around structures built on a slope in an AO zone, so that floodwater is guided around and away from the building rather than pooling against a foundation. Because shallow flooding in an AO zone behaves differently than a defined-channel flood, the Floodplain Administrator applies this depth-number-plus-freeboard formula instead of the standard Base Flood Elevation calculation used elsewhere in the county's Special Flood Hazard Areas.