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

Sec. 14-425 defines the Regulatory Flood Protection Elevation, the number that actually controls how high a structure must be built, as the Base Flood Elevation plus a two-foot freeboard. Where FEMA has determined a Base Flood Elevation for a Special Flood Hazard Area, the Regulatory Flood Protection Elevation is that BFE plus two feet; where no BFE has been established, it defaults to at least two feet above the highest adjacent grade. Freeboard exists, per the code's own definition, to cover the unknowns that can push flood heights above the modeled base flood, including wave action, blocked bridge or culvert openings, and increased runoff from watershed urbanization.

Sec. 14-440(1) applies that number directly to residential construction: new construction and substantial improvement of any residential structure, including manufactured homes, must have the reference level, including any basement, elevated no lower than the Regulatory Flood Protection Elevation. Non-residential structures get the same elevation floor under Sec. 14-440(2), or may floodproof to the same level instead. Along riverine reaches where a Base Flood Elevation exists but no floodway or non-encroachment area has been mapped yet, Sec. 14-442 layers on an added test: no fill, new construction, or other development may proceed unless a licensed North Carolina professional engineer certifies that the cumulative effect of the project, combined with all other existing and anticipated development, will not raise the base flood water surface elevation more than one foot at any point in the community.