Madison County, IL Environmental Rules: Flood Elevation Requirements (2026)

Chapter 94, Flood Damage Prevention, adopted by Ord. 2022-04, sets the county's floodplain building standard for unincorporated territory only; incorporated cities like Edwardsville and Alton administer their own floodplain rules. The base flood elevation (BFE) is taken from the Flood Insurance Study of Madison County prepared by FEMA and dated April 15, 1982, or from the flood insurance rate map for AH and AO zones. The code adds a safety margin called freeboard: the flood protection elevation (FPE) equals the BFE plus one foot. 07, any new building, substantial improvement, manufactured home placement, or repair of substantial damage in the floodplain must have its lowest floor, including the basement, at or above the FPE.

Builders can meet this three ways: constructing on permanent fill with the lowest floor at or above the FPE, elevating the building on stilts, piles, or open foundation walls with flood vents sized at one square inch per square foot of enclosed area below the BFE, or building on a FEMA-compliant crawlspace. 03's BFE data, and keeps records of as-built lowest-floor elevations and floodproofing certificates. Property owners who disagree with the mapped elevation may commission their own engineering study for the State Water Survey to consider.