Williamson County, TN Environmental Rules: Flood Elevation Requirements (2026)

04(B)(1)(a) sets the residential standard: in AE Zones where Base Flood Elevation data is available, new construction and substantial improvement of any residential building, including a manufactured home, must have the lowest floor, including basement, elevated to no lower than one foot above the Base Flood Elevation. Where solid foundation perimeter walls are used to elevate the structure, the code requires flood-vent openings sized to equalize hydrostatic pressure on both sides of the exterior walls, detailed under the Enclosures standard. 04(B)(2)(a) applies the identical one-foot-above-BFE floor requirement to commercial, industrial and other non-residential buildings, but gives owners the option to floodproof instead of elevate if the space below the required elevation is watertight, substantially impermeable, and engineered to resist hydrostatic and hydrodynamic loads, certified by a Tennessee registered professional engineer or architect.

04(B)(1)(b) and (2)(b) instead require the lowest floor at least three feet above the highest adjacent grade. 04(B)(4). A permit holder must submit an as-built Finished Construction Elevation Certificate on FEMA Form 086-0-33 to the County Engineer, acting as Administrator, before a Certificate of Compliance/Occupancy can issue; failure to submit it, or to correct deficiencies the Administrator flags, is grounds to withhold occupancy or issue a stop-work order.