St. Louis County, MO Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard
- 1 foot above base flood elevation
- Residential option
- elevate only, no floodproofing
- Non-residential option
- elevate or certify floodproofing
- AO/AH zones
- FIRM depth number or 2 ft min
- Roadways
- 1 ft above base flood elevation
- Enclosure vents
- 1 sq in per sq ft, 2+ openings
- Penalty
- up to $1,000 per day, §1008.090
Summary
Where the County has mapped a base flood elevation on a numbered A, AE, or AH zone, Section 1008.050 requires new construction and substantial improvements to elevate the lowest floor, including any basement, to at least one foot above that base flood elevation. Non-residential buildings may floodproof to that same one-foot freeboard instead, but a registered engineer or architect must certify the floodproofing meets the standard.
2. Specific standards. (1.) In all areas identified as numbered and unnumbered A zones, AE, and AH Zones, where base flood elevation data have been provided, as set forth in Section 1008.050-1(2.), the following provisions are required: (a.) Residential construction. New construction or substantial improvement of any residential structures, including manufactured homes, shall have the lowest floor, including basement, elevated to one (1) foot above base flood elevation. (b.) Non-residential construction. New construction or substantial improvement of any commercial, industrial, or other non-residential structures, including manufactured homes shall have the lowest floor, including basement, elevated to one (1) foot above the base flood elevation or, together with attendant utility and sanitary facilities, be floodproofed so that below the base flood elevation the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 85 | Traffic: Supplement 80).
Full Breakdown
020 defines "freeboard" as a factor of safety expressed in feet above a flood level, added to compensate for the many unknown factors that could push flood heights above the level calculated for a selected flood and floodway condition, such as bridge openings or the hydrological effect of watershed urbanization. 050(2)(1) sets the county's freeboard at one foot: residential structures, including manufactured homes, must have their lowest floor, including any basement, elevated to one foot above the base flood elevation, with no floodproofing alternative. 040-3(9).
New public roadways must also be built to at least one foot above base flood elevation. In AO and AH shallow-flooding zones, where no numbered base flood elevation exists, the freeboard standard shifts to the depth number printed on the FIRM, or at least two feet above the highest adjacent grade if no depth number is shown, applied the same way to residential and non-residential structures. Fully enclosed areas below the lowest floor used only for parking, building access, or storage must include flood vents: at least two openings with a combined net area of one square inch per square foot of enclosed area, with the lowest opening no higher than one foot above grade, unless a registered engineer certifies an alternative design.
Violations & Fines
Building below the required freeboard, or occupying a structure that was never elevated or floodproofed to the Section 1008.050 standard, is a violation of Chapter 1008 under Section 1008.090, punishable by a fine of up to $1,000 upon conviction, with each day of noncompliance counted as a separate offense.
Frequently Asked Questions
How much freeboard does St. Louis County require above base flood elevation?
Can a commercial building floodproof instead of elevating?
What if my lot is in an AO or AH shallow flooding zone with no base flood elevation?
What are the venting rules for enclosed areas below the elevated floor?
Sources & Official References
Other rules in St. Louis County
Compare St. Louis County to another location·View the Missouri environmental rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.