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(A) The building must be 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. Hydrostatic loads and the effects of buoyancy can usually be addressed through the required openings stated in division (B) below. Because of hydrodynamic loads, crawlspace construction is not recommended 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. Other types of foundations are recommended for these areas.
(B) The crawlspace is an enclosed area below the base flood elevation and, as such, must have openings that equalize hydrostatic pressures by allowing the automatic entry and exit of flood waters. The bottom of each flood vent opening can be no more than one foot above the lowest adjacent exterior grade.
(C) 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, or other materials that extend below the BFE. The recommended construction practice is to elevate the bottom of joists and all insulation above BFE.
(D) Any building utility systems within the crawlspace must be elevated above BFE or designed so that flood waters cannot enter or accumulate within the system components during flood conditions. Ductwork, in particular, must either be placed above the BFE or sealed from flood waters.
(E) The interior grade of a crawlspace below the BFE must not be more than two feet below the lowest adjacent exterior grade.
(F) The height of the below-grade crawlspace, measured from the interior grade of the crawlspace to the bottom of the structural support of the next higher floor must not exceed four feet at any point.
(G) There must be an adequate drainage system that removes flood waters from the interior area of the crawlspace. The enclosed area should be drained within a reasonable time after a flood event. The type of drainage system will vary because of the site gradient and other drainage characteristics, such as soil types. Possible options include natural drainage through porous, well-drained soils and drainage systems such as perforated pipes, drainage tiles, or gravel or crushed stone drainage by gravity or mechanical means.
(H) The velocity of flood waters at the site should not exceed five feet per second for any crawlspace. For velocities in excess of five feet per second, other foundation types should be used.
(Ord. 527, passed 1-14-2013)
In all special flood hazard areas, recreational vehicles that are an allowed use or structure under Chapter 155 must either:
(A) Be placed on the site for fewer than 180 consecutive days;
(B) Be fully licensed and ready for highway use, on its wheels or jacking system, attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions; or
(C) Shall:
(1) Meet the development permit requirements of §§ 153.32 and 153.50 through 153.61, the manufactured home requirement in the Oregon Manufactured Dwelling Installation Specialty Code, and be elevated on a permanent foundation such that the bottom of the vehicle chassis is elevated to or above base flood elevation; and
(2) Be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement. Methods of anchoring may include, but are not limited to, use of over-the-top or frame ties to ground anchors. Permanently placed recreational vehicles shall, in addition, meet the requirements of § 153.61(A).
(Ord. 527, passed 1-14-2013)
(A) Temporary structures placed in the floodway. Relief from no-rise evaluation, elevation, or dry flood-proofing standards may be granted for a non-residential structure placed during the dry season (June through October) and for a period of less than 90 days. A plan for the removal of the temporary structure after the dry season or when a flood event threatens shall be provided. The plan shall include disconnecting and protecting from water infiltration and damage all utilities servicing the temporary structure.
(B) Temporary storage (temporary storage does not include hazardous materials) in the floodway. Temporary storage of goods and materials is allowed in the floodway for a period of less than 90 days within the dry season (June through October).
(Ord. 527, passed 1-14-2013)
(A) Construction of new essential facilities shall be, to the extent possible, located outside the limits of the special flood hazard area. Construction of new essential facilities shall be permissible within the special flood hazard area if no feasible alternative site is available. Flood-proofing and sealing measures must be taken to ensure that toxic substances or priority organic pollutants as defined by the Oregon Department of Environmental Quality will not be displaced by or released into flood waters. The lowest floor shall be elevated three feet above the base flood elevation or to the height of the 500-year flood, whichever is higher. Access routes elevated to or above the level of the base flood elevation shall be provided to all essential facilities to the maximum extent possible.
(B) New essential and new special occupancy structures may not be constructed in the Tsunami Inundation Zone. If an exception is granted then the Coastal High Hazard Area construction standards shall apply.
(Ord. 527, passed 1-14-2013)
(A) New and replacement tanks in flood hazard areas either shall be elevated above the base flood elevation on a supporting structure designed to prevent flotation, collapse, or lateral movement during conditions of the base flood, or be anchored to prevent flotation, collapse, or lateral movement resulting from hydrostatic loads, including the effects of buoyancy assuming the tank is empty, during conditions of the design flood.
(B) New and replacement tank inlets, fill openings, outlets, and vents shall be placed a minimum of two feet above base flood elevation or fitted with covers designed to prevent the inflow of flood water or outflow of the contents of the tank during conditions of the design flood.
(Ord. 527, passed 1-14-2013)
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