St. Clair County, IL Environmental Rules: Flood Elevation Requirements (2026)

Section 13-1-2 of the County Floodplain Code defines "Flood Protection Elevation" or "FPE" as the base flood elevation plus two feet of freeboard, and Section 13-1-7 makes that FPE the protection standard for buildings in the floodplain. The two-foot buffer applies to new construction valued over $1,000 or larger than 70 square feet, repairs to a substantially damaged building, alterations that add more than 20% of floor area or equal 40% of the building's fair market value, a manufactured home placed on a new or existing site, a travel trailer or RV kept on site more than 180 days a year, and any repetitive-loss structure.

A building may meet the standard by permanent fill, with the lowest floor and all mechanical equipment at or above the FPE and fill extending at least 15 feet beyond the foundation, or by elevation on stilts, piles, or open foundation walls, with the lowest floor and all electrical, heating, plumbing, and air conditioning equipment and utility meters at or above the FPE. Enclosed areas below the FPE must allow floodwater to pass through openings sized at one square inch per square foot of enclosed area, may only be used for parking or building access, and require a recorded non-conversion agreement once the enclosure reaches four feet in height.

Manufactured homes and permanently installed travel trailers must be elevated to the FPE and tied down under the Illinois Mobile Home Tie-Down Act, 77 Ill. Adm. Code 870.