Chapter 27 Flood Plain Management

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FLOODPLAIN MANAGEMENT § 27-18 (d) Elevation and floodproofing. (1) Within Zones AE and AH: (A) For residential new construction, improvements to repetitive loss structures, and substantial improvements, the lowest floor shall be elevated to or above the base flood elevation plus a freeboard of at least one foot. (B) For nonresidential new construction, improvements to repetitive loss structures, and substantial improvements, the lowest floor shall be elevated or floodproofed to or above the base flood elevation plus a freeboard of at least one foot. If the lowest floor is below the base flood elevation plus the required freeboard, then the structure together with attendant utility and sanitary facilities shall be designed, constructed, and certified by a currently licensed professional engineer or architect in the State of Hawai`i such that: (i) The structure is watertight below the base flood elevation plus the required freeboard. (ii) The walls are substantially impermeable to the passage of water. (iii) The structural components are capable of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. (C) Within Zone AH, new construction, improvements to repetitive loss structures, and substantial improvement shall be required to provide adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures. (D) Fully enclosed areas below the lowest floor that are useable solely for parking of vehicles, building access, or storage in an area other than a basement and which are subject to flooding, shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a currently licensed professional engineer or architect or meet or exceed the following criteria: A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided. Each opening must be on different sides of the enclosed area. The bottom of all openings shall be no higher than one foot above grade. Openings may be equipped with screens, louvers, valves, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters. (2) Within Zone AO: (A) For residential new construction, improvements to repetitive loss structures, and substantial improvements, the lowest floor shall be elevated above the highest adjacent grade at least one foot above the depth number specified in feet on the FIRM, or at least three feet if no depth number is specified. 27-19