23-4-3

Floodplain

• AccessoryAccessory useA secondary activity customarily incidental to the main use of the lot — a garage, a home office. structure limits600 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.

  Accessory structures in the SFHA shall comply with the elevation requirements and other requirements of subsection 23-4-3.B or, if not elevated or dry floodproofed, shall: a. Not be used for human habitation; b. Be limited to no more than 600 square feet in total floor area; c. Be useable only for parking of vehicles or limited storage; d. Be constructed with flood damage-resistant materials below the base flood elevation; e. Be constructed and placed to offer the minimum resistance to the flow of floodwaters; f. Be anchored to prevent flotation; g. Have electrical service and mechanical equipment elevated to or above the base flood elevation; h. Shall be provided with flood openings which shall meet the following criteria: (1) There shall be a minimum of two flood openings on different sides of each enclosed area; if a building has more than one enclosure below the lowest floor, each such enclosure shall have flood openings on exterior walls. (2) The total net area of all flood openings shall be at least one square inch for each square foot of enclosed area (non-engineered flood openings), or the flood openings shall be engineered flood openings that are designed and certified by a licensed professional engineer to automatically allow entry and exit of floodwaters; the certification requirement may be satisfied by an individual certification or an Evaluation Report issued by the ICC Evaluation Service, Inc. (3) The bottom of each flood opening shall be one foot or less above the higher of the interior floor or grade, or the exterior grade, immediately below the opening. (4) Any louvers, screens or other covers for the flood openings shall allow the automatic flow of floodwaters into and out of the enclosed area.

• Flood openings requirements1 sqin/sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.

  To meet this requirement, the openings must either be certified by a professional engineer or architect or meet the following minimum design criteria: a. Provide a minimum of two openings on different sides of each enclosed area subject to flooding. b. The total net area of all openings must be at least one square inch for each square foot of enclosed area subject to flooding. c. If a building has more than one enclosed area, each area must have openings to allow floodwaters to automatically enter and exit. d. The bottom of all required openings shall be no higher than one foot above the adjacent grade. e. Openings may be equipped with screens, louvers, or other opening coverings or devices, provided they permit the automatic flow of floodwaters in both directions. f. Foundation enclosures made of flexible skirting are not considered enclosures for regulatory purposes, and, therefore, do not require openings. Masonry or wood underpinning, regardless of structural status, is considered an enclosure and requires openings as outlined above.

• Manufactured homeManufactured homeA dwelling built in a factory to a federal standard and transported to the site. standards

  In zones A, AE, AH, and AO, all manufactured homes placed, or substantially improved, on individual lots or parcels, must meet all the requirements for new construction, including the elevation and anchoring requirements in subsection 23-3-1.A.6 and subsections 23-4-2 and 23-4-3.

• Non-residential elevation or floodproofing1 ft

  New construction or substantial improvement of any commercial, industrial, or non-residential building (or manufactured home) shall have the bottom of the lowest horizontal structural member of the lowest floor, including basement, elevated to or above the base flood level. ... Non-residential buildings located in all A1-30, AE, and AH zones may be floodproofed in lieu of being elevated provided that all areas of the building components below the elevation corresponding to the BFE plus one foot are water tight with walls substantially impermeable to the passage of water, and use structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy.

• Residential lowest floor elevation to or above BFE

  New construction or substantial improvement of any residential structure (including manufactured homes) in Zones A1-30, AE, AH, and A with detailed base flood elevations shall have the bottom of the lowest horizontal structural member of the lowest floor, including basement, elevated to or above the base flood level.

• Space below lowest floor restrictions

  In zones A, AE, AH, AO, and A1-A30, fully enclosed areas, of new construction or substantially improved structures, which are below the regulatory flood protection elevation shall: 1. Not be designed or used for human habitation, but shall be used solely for parking of vehicles, building access, or limited storage of maintenance equipment used in connection with the premises. Access to the enclosed area shall be the minimum necessary to allow for parking of vehicles (garage door) or limited storage of maintenance equipment (standard exterior door), or entry to the living area (stairway or elevator). 2. Be constructed entirely of flood resistant materials below the regulatory flood protection elevation; 3. Include measures to automatically equalize hydrostatic flood forces on walls by allowing for the entry and exit of floodwaters.