Bonneville County, ID Environmental Rules: Flood Elevation Requirements (2026)

Section 154.02 defines FREEBOARD as 'a factor of safety usually expressed in feet above a flood level for the purposes of floodplain management,' meant to compensate for unknown factors such as wave action, obstructed bridge openings, debris and ice jams, and the hydrologic effects of urbanization that can push flood heights above the calculated base flood elevation. The same definition sets the number: the base flood elevation (BFE) plus the freeboard establishes the flood protection elevation (FPE), and freeboard shall be one foot.

Section 154.46 applies that flood protection elevation to construction standards in special flood hazard areas where BFE data exists. New construction or substantial improvement of a residential structure, including manufactured homes, tiny homes and park models, must have its lowest floor, including the basement, and its utilities and ductwork, elevated no lower than the flood protection elevation, meaning one foot above the mapped base flood elevation. Nonresidential construction faces the same elevation floor, but § 154.46(B) gives commercial, industrial and other nonresidential structures in Zones A, AE, AH and AO the option to floodproof to the flood protection elevation instead of physically elevating, provided the structure is watertight below that line and a registered engineer or architect certifies the floodproofing meets the standard. New or replacement manufactured homes must also be securely anchored to resist flotation and lateral movement, either through an engineered foundation or the state's manufactured home installation standard, with an engineering certification required once the chassis elevation exceeds 36 inches above grade.