Hawaii County, HI Environmental Rules: Flood Zones (2026)

HCC § 27-18 sets the construction standards for special flood hazard areas identified on the county's flood insurance rate maps. New construction, substantial improvements, and repetitive-loss repairs must be anchored to resist flotation and lateral movement, built with flood-damage-resistant materials, and have utilities such as furnaces, water heaters, and electrical panels placed above the base flood elevation plus required freeboard. In Zones AE and AH, residential lowest floors must be elevated to or above the base flood elevation plus at least one foot of freeboard; nonresidential structures may instead be floodproofed to that same level if a licensed Hawaiʻi engineer or architect certifies the structure is watertight and can resist hydrostatic and hydrodynamic loads.

In Zone AO, the lowest floor must clear the highest adjacent grade by at least the FIRM's depth number plus one foot, or three feet if no depth number is given. Enclosed areas below the lowest floor used only for parking, access, or storage must have flood vents totaling at least one square inch of net opening per square foot of enclosed area, on at least two different walls, with openings no higher than one foot above grade. Within a floodway, encroachments including fill are barred unless a licensed civil engineer certifies no increase in base flood elevation; in Zones V and VE, fill cannot be used for structural support at all, and those zones instead follow the coastal high hazard standards of § 27-23.

Every new or substantially improved structure in a special flood hazard area must carry the certification required by § 27-17. Hawaii County's Department of Public Works administers this chapter under the Director as floodplain administrator, and the article's variance and appeal procedures run through §§ 27-27 through 27-31.