In all areas of special flood hazards where base flood elevation data have been provided as set forth in subsection 5-2-3B or 5-2-4-2B2 of this chapter, the following standards are required. These specific standards shall apply in addition to the general standards contained in section 5-2-5-1 of this chapter:
A. Flood Openings:
1. Flood Openings: All new construction and substantial improvements with fully enclosed areas below the lowest floor (excluding basements) are subject to the following requirements. Enclosed areas below the base flood elevation, including a crawl space shall:
a. Be designed to automatically equalize hydrostatic flood forces on walls by allowing for the entry and exit of floodwaters.
b. Be used solely for parking, storage, or building access.
c. Be certified by a registered professional engineer or architect or meet or exceed the following minimum criteria:
(1) A minimum of two (2) openings.
(2) The total net area of non-engineered openings shall be not less than one (1) square inch for every square foot of enclosed area, where the enclosed area is measured on the exterior of the enclosed walls.
(3) The bottom of all openings shall be no higher than one (1) foot above grade.
(4) Openings may be equipped with screens, louvers, valves or other coverings or devices provided that they permit the automatic flow of floodwater into and out of the enclosed areas and shall be accounted for in the determination of the net open area.
(5) All additional higher standards for flood openings in the State of Oregon Residential Specialty Codes Section R322.2.2 shall be complied with when applicable.
B. Garages:
1. Attached garages may be constructed with the garage floor slab below the base flood elevation (BFE) in riverine flood zones, if the following requirements are met:
a. If located within a floodway the proposed garage must comply with the requirements of section 5-2-5-3;
b. The floors are at or above grade on not less than one (1) side;
c. The garage is used solely for parking, building access, and/or storage;
d. The garage is constructed with flood openings in compliance with section 5-2-5-2A to equalize hydrostatic flood forces on exterior walls by allowing for the automatic entry and exit of floodwater;
e. The portions of the garage constructed below the BFE are constructed with materials resistant to flood damage;
g. The garage is constructed with electrical, and other service facilities located and installed so as to prevent water from entering or accumulating within the components during conditions of the base flood.
C. Before Regulatory Floodway: In areas where a regulatory floodway has not been designated, no new construction, substantial improvement, or other development (including fill) shall be permitted within Zones A1-30 and AE on the community’s flood insurance rate map (FIRM), unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than one (1) foot at any point within the community.
D. Residential Construction:
1. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to or above one foot (1') above base flood elevation.
2. Enclosed areas below the lowest floor shall comply with the flood opening requirements in section 5-2-5-2A.
E. Nonresidential Construction:
1. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall:
a. Have the lowest floor, including basement, elevated to the level of one foot (1') above the base flood elevation (BFE);
Or, together with attendant utility and sanitary facilities, shall:
b. Be flood-proofed so that below the base flood level the structure is watertight with walls substantially impermeable to the passage of water.
c. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy.
d. 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 section based on their development and/or review of the structural design, specifications and plans. Such certifications shall be provided to the floodplain administrator as set forth in subsection 5-2-4-2B of this Chapter.
2. Nonresidential structures that are elevated, not floodproofed, shall comply with the standards for enclosed areas below the lowest floor in section 5-2-5-2A.
3. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are one foot (1') below the floodproofed level (e.g., a building constructed to the base flood level will be rated as 1 foot below that level).
4. Applicants shall supply a maintenance plan for the entire structure to include but not limited to: exterior envelope of structure; all penetrations to the exterior of structure; all shields, gates, barriers, or components designed to provide flood proofing protection to the structure; all seals or gaskets for shields; gates, barriers, or ocmponents; and, the location of all shields, gates, barriers, and components, as well as all associated hardware, and any materials or specialized tools necessary to seal the structure.
5. Applicants shall supply an emergency action plan (EAP) for the installation and sealing of the structure prior to a flooding event that clearly identifies what triggers the EAP and who is responsible for enacting the EAP.
F. Manufactured Dwellings:
1. New or substantially improved manufactured dwellings supported on solid foundation walls shall be constructed with flood openings that comply with section 5-2-5-2A;
2. The bottom of the longitudinal chassis frame beam shall be at or above base flood elevation;
3. New or substantially improved manufactured dwellings shall be anchored to prevent flotation, collapse, and lateral movement during the base flood. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors (Reference FEMA’s “Manufactured Home Installation in Flood Hazard Areas” guidebook for additional techniques); and
4. Electrical crossover connections shall be a minimum of twelve (12) inches above base flood elevation (BFE).
G. Recreational Vehicles: Recreational vehicles placed on sites are required to:
1. Be on the site for fewer than one hundred eighty (180) days; and
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 section 5-2-5-2D including the anchoring and elevation requirements for manufactured dwellings.
H. Appurtenant (Accessory) Structures: Relief from elevation or flood proofing requirements for residential and non-residential structures in Riverine (non-coastal) flood zones may be granted for appurtenant structures that meet the following requirements:
1. Appurtenant structures located partially or entirely within the floodway must comply with requirements for development within a floodway found in section 5-2-5-3.
2. Appurtenant structures must only be used for parking, access, and/or storage and shall not be used for human habitation.
3. In compliance with State of Oregon Specialty Codes, appurtenant structures on properties that are zoned residential are limited to one-story structures less than two hundred (200) square feet, or four hundred (400) square feet if the property is greater than two (2) acres in area and the proposed appurtenant structure will be located a minimum of twenty (20) feet from all property lines. Appurtenant structures on properties that are zoned as non- residential are limited in size to one hundred twenty (120) square feet.
4. The portions of the appurtenant structure located below the base flood elevation must be built using flood resistant materials.
5. The appurtenant structure must be adequately anchored to prevent flotation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood.
6. The appurtenant structure must be designed and constructed to equalize hydrostatic flood forces on exterior walls and comply with the requirements for flood openings in section 5-2-5-2A.
7. Appurtenant structures shall be located and constructed to have low damage potential.
8. Appurtenant structures shall not be used to store toxic material, oil, or gasoline, or any priority persistent pollutant identified by the Oregon Department of Environmental Quality unless confined in a tank installed in compliance with section 5-2-5-1E.
I. Below-Grade Crawl Spaces:
1. A building must be designed and adequately anchored to resist flotation, collapse, and lateral movement of the structures 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 flood openings stated in 5-2-5-2A. Because of hydrodynamic loads, crawlspace construction is not allowed in areas with flood velocities greater than five (5) 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.
2. The crawlspace is an enclosed area below the base flood elevation (BFE) and, as such, must have openings that equalize hydrostatic pressures by allowing the automatic entry and exist of floodwaters. The bottom of each flood vent opening can be no more than one (1) foot above the lowest adjacent exterior grade.
3. 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 the joists and all insulation, or other materials that extend below the BFE. The recommended construction practice is to elevate the bottom of the joists and all insulation above the BFE.
4. Any building utility system within the crawlspace must be elevated above BFE or designed so that the floodwaters cannot enter or accumulate within the system components during flood conditions. Ductwork, in particular, must either be placed above the BFE or sealed from floodwaters.
5. The interior grade of a crawlspace below the BFE must not be more than two (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 four (4) feet at any point. The height limitation is the maximum allowable unsupported wall height according to 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 shall not exceed five (5) feet per second for the crawlspace. For velocities in excess of five (5) feet per second, other foundation types should be used. (Ord. 54, 3-24-1987; amd. Ord. 147, 4-14-2004; Ord. 219, 11-13-2019)