15.15.180 Specific standards.
In all areas of special flood hazards where base flood elevation data has been provided as set forth in TMC 15.15.070, Basis for establishing the areas of special flood hazard, or TMC 15.15.140(B), Use of Other Base Flood Data, the following provisions are required:
A. Residential Construction.
1. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated two feet 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. A registered professional engineer or architect must either certify designs for meeting this requirement or meet or exceed the following minimum criteria:
a. A minimum of two 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 one foot above grade.
c. Openings may be equipped with screens, louvers, or other coverings or devices if 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 a basement floor, elevated two feet above the base flood elevation; or, together with the requirements for utility and sanitary facilities set out below, shall:
1. Be floodproofed so that below the flood protection level (two feet above 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 licensed in the state of Oregon 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 floodplain administrator, as set forth in TMC 15.15.140;
4. Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in subsection (A) of this section;
5. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are one foot below the floodproofed level (e.g., a building floodproofed to the base flood level will be rated as one foot below).
C. Manufactured Homes. All manufactured homes to be placed or substantially improved on sites within an A Zone on the community’s FIRM shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated two feet above the base flood elevation 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 within an A Zone on the community’s FIRM shall either:
1. Be on the site for fewer than 180 consecutive days and be fully licensed and ready for highway use; be on its wheels or jacking system, and be attached to the site only by quick disconnect type utilities and security devices, with no permanently attached additions; or
2. Meet the requirements of subsection (C) of this section, including the elevation and anchoring requirements for manufactured homes.
E. Accessory Structures. Relief from elevation or floodproofing requirements for residential and nonresidential structures in riverine (noncoastal) flood zones may be granted for appurtenant or accessory structures that meet the following requirements:
1. Accessory structures located partially or entirely within the floodway must comply with requirements for development within a floodway found in TMC 15.15.190.
2. Accessory 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, accessory structures on properties that are zoned residential are limited to one-story structures less than 200 square feet, or 400 square feet if the property is greater than two acres in area and the proposed accessory structure will be located a minimum of 20 feet from all property lines. Accessory structures on properties that are zoned as nonresidential are limited in size to 120 square feet.
4. The portions of the accessory structure located below the base flood elevation must be built using flood resistant materials.
5. The accessory 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 accessory structure must be designed and constructed to equalize hydrostatic flood forces on exterior walls and comply with the requirements for flood openings in subsection (A) of this section.
7. Accessory structures shall be located and constructed to have low damage potential.
8. Accessory 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 TMC 15.15.170(C).
9. Accessory structures constructed with electrical, mechanical, and other service facilities shall be located and installed to prevent water from entering or accumulating within the components during conditions of the base flood. [Ord. 979 § 1 (Exh. A), 2023; Ord. 916 § 5.2, 2016; Ord. 859 § 1; Ord. 752 § 5.2. Formerly 15.15.170.]