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

Section 14-502 of the Bonner County Revised Code sets the specific elevation standards where Base Flood Elevation data has been provided. The Base Flood Elevation (BFE) is the water surface elevation of the flood with a one percent chance of being equaled or exceeded in any given year. Chapter 2 defines the Flood Protection Elevation (FPE) as the BFE plus the freeboard: one foot of freeboard where a BFE has been determined, and at least two feet above the highest adjacent grade where none has been established.

Residential construction, including manufactured homes, must have the lowest floor, including basement, elevated no lower than one foot above the BFE. Fully enclosed areas below that floor are prohibited or must have automatic flood openings: at least two openings on different walls, a total net area of not less than one square inch for every square foot of enclosed area, and the bottom of every opening no higher than one foot above grade. A licensed professional engineer or architect certifies the design, and materials at or below the FPE must withstand direct contact with floodwaters for at least seventy-two hours.

Non-residential buildings follow the same one-foot rule, but in Zones A, AE, AH, AO and A1-30 they can instead be floodproofed to one foot above the BFE with watertight walls, certified by an engineer or architect. Below grade crawl spaces cannot have an interior grade more than two feet below the lowest adjacent exterior grade, cannot exceed four feet in height, must drain within seventy-two hours, and are prohibited where floodwater velocity exceeds five feet per second. New and replacement manufactured homes must sit with the lowest floor no lower than the FPE, and a chassis more than thirty-six inches above grade needs an engineering certification. Where a site has more than one base flood elevation, the highest BFE applies (§ 14-501.Q).