Every new or substantially improved nonresidential structure must be either:elevated to at least the flood-protection elevation; or dry or wet floodproofed. Basements are prohibited for any new nonresidential structure in the tidal and nontidal floodplains. Every new or substantially improved nonresidential structure must meet the requirements of <cite data-path="|7|§3-14">§ 3-14 {“Enclosures below lowest floor or flood-protection elevation”} of this subtitle</cite>. The elevation of the lowest floor of the improvement must be certified on an elevation certificate after the lowest floor is in place. In mixed-use structures, areas below the flood-protection elevation may not be used for residential use even if the area is floodproofed. Floodproofing designs for existing structures must ensure that areas below the flood- protection elevation are watertight with walls substantially impermeable to the passage of water and with structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy, as described in <cite data-path="|7|§1-3|(a)">§ 1-3(a) {“Definitions: Floodproofing”} of this Division I</cite>. If the floodproofing option is chosen, a floodproofing certificate must be completed by a licensed professional engineer or professional architect who has reviewed the design and specifications and certifies that the nonresidential structure will meet this standard. A Use and Occupancy permit cannot be approved until the floodproofing certificate is submitted. In tidal and nontidal floodplains, any horizontal expansion that increases the footprint and that is less than substantial must also have the lowest floor elevated to at least the flood-protection elevation. City Code, 1976/83, art. 7, §5(a)(3-a) 2000, art. 7, §3-5 Ord. 92-134 Ord. 11-516 Ord. 14-208 Ord. 21-020