New construction and substantial improvements built on a crawlspace or a subgrade (below grade) crawlspace may be permitted if the development is designed and meets or exceeds the standards found in FEMA’s Technical Bulletins 1, 2 and 11, which include, but are not limited to, the following:
(A) The structure must be affixed to a permanent foundation, designed and adequately anchored to resist flotation, collapse and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. Because of hydrodynamic loads, crawlspace construction is not allowed in areas with flood velocities greater than five feet per second unless the design is reviewed by a qualified design professional, such as a registered architect or professional engineer;
(B) The crawlspace is an enclosed area below the BFE and, as such, must have openings that equalize hydrostatic pressures by allowing the automatic entry and exit of floodwaters. The bottom of each flood vent opening can be not more than one foot above the LAG;
(C) The crawlspace enclosure must have proper openings that allow the equalization of hydrostatic pressure by allowing automatic entry and exit of floodwaters. To achieve this, a minimum of one square inch of flood opening is required per one square foot of the enclosed area subject to flooding;
(D) Portions of the building below the BFE must be constructed with materials resistant to flood damage. This includes not only the foundation walls of the crawlspace used to elevate the building, but also any joists, insulation, piers or other materials that extend below the BFE. Ductwork, in particular, must either be placed above the BFE or scaled from floodwaters;
(E) Any building utility systems within the crawlspace must be elevated above the BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions;
(F) The interior grade of a crawlspace below the BFE must not be more than two feet below the LAG;
(G) The height of the below-grade crawlspace, measured from the lowest interior grade of the crawlspace floor to the bottom of the floor joist of the next higher floor, cannot exceed four feet at any point;
(H) There must be an adequate drainage system that removes floodwaters from the interior area of the crawlspace. The enclosed area should be drained within a reasonable time after a flood event; and
(I) Buildings with below-grade crawlspaces will have higher flood insurance premiums than buildings that have the preferred crawlspace construction, with the interior elevation at or above the LAG.
(Ord. 2020-12-1, passed 12-14-2020)