Washington County, UT Environmental Rules: Flood Elevation Requirements (2026)

Section 12-5-2 of the Washington County Code sets specific construction standards for any area of special flood hazard where base flood elevation data has been provided under section 12-4-1. For residential construction, subsection A requires new construction and substantial improvements to have the lowest floor, including any basement, elevated a minimum of two feet above the base flood elevation, with certification by a registered professional engineer or architect that the design and construction methods meet accepted standards; that certification goes to the floodplain administrator under section 12-4-3.

Nonresidential structures under subsection B may instead be floodproofed so the structure is watertight below the base flood elevation, with walls substantially impermeable to water and structural components able to resist hydrostatic and hydrodynamic loads, again certified by a licensed engineer or architect. Subsection C requires enclosed areas below the lowest floor used only for parking, building access or storage to include flood vents: at least two openings with a total net area of no less than one square inch per square foot of enclosed area, with the bottom of openings no higher than one foot above grade, so floodwaters can enter and exit automatically and equalize hydrostatic pressure on the walls.

Manufactured homes placed in FIRM zones A1-30, AH and AE must also be elevated so the lowest floor sits at least two feet above base flood elevation and be anchored to a permanent foundation system resisting flotation, collapse and lateral movement, per subsection D. These freeboard and floodproofing standards apply on top of, not instead of, the development permit process in section 12-4-1, and all elevation certificates become part of the county's permanent floodplain record.