Jefferson County, TX Environmental Rules: Flood Elevation Requirements (2026)

Appendix 5 of the Jefferson County Subdivision and Development Regulations, the county's Flood Damage Prevention Order, sets the freeboard standard for the unincorporated area. 2-1(1), new construction and substantial improvement of any residential structure in Zones A1-30, AH and AE must have the lowest floor, including any basement, elevated above the base flood elevation shown on the effective Flood Insurance Rate Map, plus one additional foot of freeboard. Fully enclosed areas below that lowest floor that are subject to flooding are prohibited unless engineered to automatically equalize hydrostatic pressure, meeting minimum criteria such as two openings totaling at least one square inch of net area per square foot of enclosed space, with opening bottoms no higher than one foot above grade.

2-2 may instead be flood-proofed watertight to one foot above BFE, certified by a registered professional engineer or architect, with a Floodproofing Certificate filed in Appendix 3. 2-3 must be elevated on a permanent foundation so the lowest floor sits at or above BFE plus one foot and is securely anchored against flotation and lateral movement. 3-2 directs the Floodplain Administrator, the Jefferson County Engineer, to obtain and use the best available federal, state or other elevation data. 1-1.