St. Charles County, MO Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Residential freeboard
- 1 foot above base flood elevation
- Non-residential option
- Dry-floodproof with PE certification
- Permit required
- Floodplain development permit, § 405.325
- Substantial improvement trigger
- 50% of current market value
- Appeal body
- Board of Zoning Adjustment, 45-day ruling
- Max fine
- $500/day or 6 months jail
Summary
New homes and additions in unincorporated St. Charles County's mapped Zone A and Zone AE must sit with the lowest floor, including any basement, elevated one foot above base flood elevation. Non-residential buildings can dry-floodproof instead, but only with a licensed engineer's certification and a floodplain development permit from Planning and Zoning.
1. Require that all new construction and substantial improvements of residential structures, including manufactured homes within Zone A and Zone AE on the County's FIRM, have the lowest floor (including basement) elevated to one (1) foot above the base flood elevation. 2. Require that all new construction and substantial improvements of non-residential structures within Zone A and Zone AE on the County's FIRM have the lowest floor (including basement) elevated one (1) foot above the base flood elevation or, together with attendant utility and sanitary facilities, be designed so that below one (1) foot above the base flood level 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. A registered professional engineer shall certify that the standards of this Subsection are satisfied.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4863880; v61 updated 2026-05-11; through 05-11-2026).
Full Breakdown
320(B)(7). Enclosed areas below the lowest floor used only for parking, access, or storage must have at least two openings in two different walls, one square inch of net opening for every square foot of enclosed area, with the bottom of each opening no higher than one foot above grade. 325, and that permit must show the existing base flood elevation, the proposed elevation of the structure and its mechanical components, and the current market value of the structure as determined by the County Assessor. 335 forces full compliance with the one-foot freeboard standard, including elevation of electrical, heating, and plumbing equipment. 315.
Violations & Fines
Building below the required one-foot freeboard or starting work without a floodplain development permit draws a written stop-work order from the Director of the Division of Planning and Zoning under Section 405.645. Ignoring that order is a misdemeanor punishable by a fine of up to five hundred dollars per day or up to six months in the County Jail, and Section 405.655 makes every day the violation continues a separate offense. The County, the Prosecuting Attorney, or an affected property owner can also sue in Circuit Court to force removal or correction of non-compliant construction under Section 405.650.
Frequently Asked Questions
How high above base flood elevation must a new house be built?
Can a business building skip the elevation requirement?
Do I need a permit to rebuild after flood damage?
What happens if my floodplain permit is denied?
Sources & Official References
Other rules in St. Charles County
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