Idaho Falls, ID Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard
- 1.5 feet above BFE
- No-BFE standard
- 1.5 ft above highest adjacent grade
- Residential floor
- Must sit at or above FPE
- Non-residential option
- Floodproof to FPE instead
- Code sections
- 10-4-2, 10-4-5(B)(1)
Summary
Idaho Falls sets the Flood Protection Elevation at the Base Flood Elevation plus 1.5 feet of freeboard, and new residential construction in Special Flood Hazard Areas must have its lowest floor built to that elevation.
Flood Protection Elevation (FPE): the Base Flood Elevation plus the Freeboard.
a. In "Special Flood Hazard Areas" where Base Flood Elevations (BFEs) have been determined, this elevation shall be the BFE plus one and a half (1.5) feet of freeboard; and
b. In "Special Flood Hazard Areas" where no BFE has been established, this elevation shall be at least one and a half (1.5) feet above the highest adjacent grade.
Flood Protection System: those physical structural works for which funds have been authorized, appropriated, and expended and which have been constructed specifically to modify flooding in order to reduce the extent of the area within a community subject to a "special flood hazard" and the extent of the depths of associated flooding. Such a system typically includes dams, reservoirs, levees, or dikes. These specialized flood modifying works are those constructed in conformance with sound engineering standards.
Floodway: the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation.
CITY CODE OF THE CITY OF IDAHO FALLS 593 Freeboard: a factor of safety usually expressed in feet above a flood level for the purposes of floodplain management. Freeboard tends to compensate for the many unknown factors that could
Full Breakdown
City Code section 10-4-2 defines the Flood Protection Elevation as the Base Flood Elevation plus 1.5 feet of freeboard where a BFE has been determined, or 1.5 feet above the highest adjacent grade where no BFE has been established. Section 10-4-5(B)(1) then requires new construction, substantial improvements, and manufactured homes in a Special Flood Hazard Area to have the lowest floor, including any basement, elevated no lower than that Flood Protection Elevation. Non-residential structures may floodproof to the same elevation instead of elevating, with certification from a registered engineer or architect.
Violations & Fines
Building below the required Flood Protection Elevation violates Chapter 10-4 and is a misdemeanor, punishable by a fine, up to 180 days imprisonment, or both.
Frequently Asked Questions
How much freeboard does Idaho Falls require above base flood elevation?
Does a new house have to be built above the Flood Protection Elevation?
Sources & Official References
Other rules in Idaho Falls
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