A. Residential construction.
1. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to a minimum of one foot above the base flood elevation.
2. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or 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 be either certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria:
a. A minimum of 2 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.
b. The bottom of all openings shall be no higher than 1 foot above grade.
c. Openings may be equipped with screens, louvers, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.
B. Nonresidential construction. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall either have the lowest floor, including basement, elevated at or above the base flood elevation; or together with attendant utility and sanitary facilities, shall:
1. Be floodproofed so that below the base flood level the structure is watertight with walls substantially impermeable to the passage of water.
2. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy.
3. Be certified by a registered professional engineer or architect that the design and methods of construction are in accordance with accepted standards of practice for meeting provisions of this subsection based on their development and/or review of the structural design, specifications, and plans. Such certifications shall be provided to the official.
4. Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in § 15.12.150.A.2.
5. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are 1 foot below the floodproofed level (e.g., a building floodproofed to the base flood level will be rated as 1 foot below).
C. Manufactured homes.
1. All manufactured homes to be placed or substantially improved on sites that are:
a. Outside of a manufactured home park or subdivision, or
b. In a new manufactured home park or subdivision, or
c. In an expansion to an existing manufactured home park or subdivision, or
d. In an existing manufactured home park or subdivision on which a manufactured home has incurred "substantial damage" as the result of a flood;
e. Shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated to a minimum of 1 foot above the base flood elevation and be securely anchored to an adequately designed foundation system to resist flotation, collapse, and lateral movement.
2. Manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision within Zones A1-30, AH, and AE on the community's FIRM that are not subject to the above manufactured home provisions be elevated so that either:
a. The lowest floor of the manufactured home is elevated to a minimum of 1 foot above the base flood elevation; or
b. The manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than 36 inches in height above grade and be securely anchored to an adequately designed foundation system to resist flotation, collapse, and lateral movement.
D. Recreational vehicles. Recreational vehicles placed on sites are required to either:
1. Be on the site for fewer than 180 consecutive days.
2. Be fully licensed and ready for highway use, on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and security devices, and has no permanently attached additions; or
3. Meet the requirements of § 15.12.150.C and the elevation and anchoring requirements for manufactured homes.
E. Below-grade crawl spaces. Below-grade crawlspaces are allowed subject to the following standards as found in FEMA Technical Bulletin 11-01, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas.
1. 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 § 15.12.150.E.2 below. Because of hydrodynamic loads, crawlspace construction is not allowed in areas with flood velocities greater than 5 feet per second unless the design is reviewed by a qualified design professional, such as a registered architect or professional engineer.
2. 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 floodwaters. The bottom of each flood vent opening can be no more than 1 foot above the lowest adjacent exterior grade.
3. Portions of the building below the base flood elevation 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 base flood elevation. The recommended construction practice is to elevate the bottom of joists and all insulation above the base flood elevation.
4. Any building utility systems within the crawlspace must be elevated above base flood elevation or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions. Ductwork in particular must either be placed above the base flood elevation or sealed from floodwaters.
5. The interior grade of a crawlspace below the base flood elevation must not be more than 2 feet below the lowest adjacent exterior grade.
6. The height of the below-grade crawlspace, measured from the interior grade of the crawlspace to the top of the crawlspace foundation wall must not exceed 4 feet at any point. The height limitation is the maximum allowable unsupported wall height according to the engineering analyses and building code requirements for flood hazard areas.
7. 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. 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.
8. The velocity of floodwaters at the site should not exceed 5 feet per second for any crawlspace. For velocities in excess of 5 feet per second, other foundation types should be used.
9. For more detailed information refer to FEMA Technical Bulletin 11-01.
(Ord. 1279, passed 6-18-2008)