Building rules for flood-prone areas

Standards for construction within areas of special flood hazards are established as follows: (a) Anchoring. (1) New construction, improvements to repetitive loss structures, and substantial improvements shall be adequately anchored to resist flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. (2) All manufactured homes, including mobile homes, shall meet all standards for structures. (b) Construction materials and methods. (1) New construction, improvements to repetitive loss structures, and substantial improvement shall be constructed with materials and utility equipment resistant to flood damage. (2) New construction, improvements to repetitive loss structures, and substantial improvement shall be constructed using methods and practices that minimize flood damage. 27-17 SUPP. 3 (1-2018) (3) New construction, improvements to repetitive loss structures, and substantial improvement shall be designed and constructed with electrical, heating, ventilation, plumbing, air-conditioning equipment, and other service facilities including, but not limited to, furnaces, heat pumps, water heaters, washers, dryers, elevator lift equipment, electrical junction boxes, circuit breaker boxes, and food freezers located above the base flood elevation plus any required freeboard. (4) Within Zones V and VE, new construction, improvements to repetitive loss structures, and substantial improvements shall comply with the standards of section 27-23. (5) Recreational vehicles placed on sites within Zones AH and AE on the FIRM shall be elevated and anchored or be on the site for less than one hundred eighty consecutive days or be fully licensed and highway ready. (c) Encroachments. (1) Within a floodway, encroachments (including fill), new construction, improvements to repetitive loss structures, substantial improvements, and other developments, shall be prohibited unless certified by a professional civil engineer licensed in the State of Hawai‘i, with supporting data, that the encroachment will not cause any increase in base flood elevations during the occurrence of the base flood discharge. (2) Require, until a regulatory floodway is designated, that no new construction, improvements to repetitive loss structures, substantial improvements, or other development (including fill), shall be permitted within Zones AE on the FIRM, unless demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood at any point. (3) Within all zones of special flood hazards, but not including floodways, filling which would result in the blockage or impediment of flow and/or induce or aggravate flooding shall be prohibited unless certified by a professional civil engineer licensed in the State of Hawai‘i, with supporting data, that the encroachment will not cause any increase in base flood elevations during the occurrence of the base flood discharge. (4) Within floodway fringe areas, filling to elevate the lowest floor of a nonresidential structure may only be permitted where the structure: (A) Is floodproofed so that below the base flood elevation plus any required freeboard the structure is watertight with walls substantially impermeable to the passage of water, and (B) Has structural components capable of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. (5) In Zones V and VE, use of fill for structural support of buildings shall be prohibited. 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. (B) For nonresidential new construction, improvements to repetitive loss structures, and substantial improvements, the lowest floor shall be elevated or completely floodproofed 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. If the lowest floor is to be completely floodproofed, then a currently licensed professional engineer or architect in the State of Hawai‘i shall develop and/or review structural design, specifications and plans for construction and shall certify that the design and methods of construction are in accordance with accepted standards of practice for the structure together with attendant utility and sanitary facilities such that: (i) The structure is watertight below the referenced flood elevation. (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) 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. (3) Within Zones V and VE: New construction, improvements to repetitive loss structures, and substantial improvement shall comply with the standards of section 27-23. (4) Within Zone A: New construction, improvements to repetitive loss structures, and substantial improvement shall comply with the standards of section 27-24. (e) Certification requirements. All new construction, improvements to repetitive loss structures, and substantial improvement within areas of special flood hazard shall be certified as required by the standards of section 27-17. (1993, ord 93-78, sec 3; am 1997, ord 97-116, sec 3; am 2007, ord 07-169, sec 11; am 2010, ord 10-115, sec 5.)27-18