Skip to code content (skip section selection)
A. Subdivision Standards:
1. All subdivision proposals shall be consistent with the need to minimize flood damage.
2. All subdivision preliminary plats/development plans shall include the mapped flood hazard zones from the effective FIRM.
3. Base flood elevation data shall be generated and/or provided for subdivision proposals and all other proposed development, including manufactured home parks and subdivisions, greater than fifty (50) lots or five (5) acres, whichever is less.
4. All subdivisions shall have public utilities and facilities such as sewer, gas, electric and water systems located and constructed to minimize flood damage.
5. All subdivisions shall have adequate drainage provided to reduce exposure to flood hazards.
B. Construction Standards: In all areas of special flood hazard the following provisions are required:
1. New construction and substantial improvements of an existing structure, including a structure that has been substantially damaged, shall be anchored to prevent flotation, collapse or lateral movement of the structure.
2. New construction and substantial improvements of an existing structure, including a structure that has been substantially damaged, shall be constructed with materials and utility equipment resistant to flood damage and by methods and practices that minimize flood damage.
3. All new construction or substantial improvements of an existing structure, including a structure that has been substantially damaged, that includes a fully enclosed area located below the lowest floor formed by the foundation and other exterior walls shall be designed to be an unfinished or flood resistant enclosure. The enclosure shall be designed to equalize hydrostatic flood forces on exterior walls by allowing for the automatic entry and exit of floodwater. Designs for complying with this requirement must be certified by a licensed professional engineer or architect or meet the following minimum criteria:
a. Provide a minimum of two (2) openings with:
(1) A total net area of not less than one square inch for every square foot of enclosed area subject to flooding;
(2) The bottom of all openings shall be no higher than one foot (1') above the higher of the exterior or interior grade or floor immediately below the opening;
(3) Openings may be equipped with screens, louvers, valves or other coverings or devices provided they permit the automatic flow of floodwater in both directions without manual intervention.
b. To comply with the "lowest floor" criteria of this chapter, the unfinished or flood resistant enclosure shall only be used for parking of vehicles, limited storage of maintenance equipment used in connection with the premises, or entry to the elevated area.
c. The interior portion of such enclosed area shall not be partitioned or finished into separate rooms.
d. For crawl space foundation types, construction must follow the guidelines in FEMA TB 11-01, crawl space construction for structures located in special flood hazard areas: national flood insurance program interim guidance, specifically:
(1) Below grade crawl spaces are prohibited at sites where the velocity of floodwaters exceed five feet (5') per second;
(2) Interior grade of the crawl space below the BFE must not be more than two feet (2') below the lowest adjacent exterior grade (LAG);
(3) Height of the below grade crawl space, measured from the lowest interior grade of the crawl space to the bottom of the floor joist must not exceed four feet (4') at any point;
(4) Contain an adequate drainage system that removes floodwaters from the interior area of the crawl space.
4. All heating and air conditioning equipment and components, all electrical, ventilation, plumbing, and other facilities shall be designed and/or elevated to prevent water from entering or accumulating within the components during flooding.
5. New and replacement water supply systems shall be designed to minimize or to eliminate infiltration of floodwaters into the system.
6. New and replacement sanitary sewage systems shall be designed to minimize or to eliminate infiltration of floodwaters into the systems and discharges from the systems into floodwaters.
7. On site waste disposal systems shall be located and constructed to avoid functional impairment, or contamination from them, during flooding.
8. Any alteration, repair, reconstruction or improvement to a structure that is not compliant with the provisions of this chapter, shall be undertaken only if the nonconformity is minimal in order to meet health and safety standards.
C. Manufactured Home Standards: In all areas of special flood hazard where the flood protection elevation is established, these standards for manufactured homes and recreational vehicles that are an allowed use under the zoning ordinance shall apply:
1. Manufactured homes placed or substantially improved:
a. On individual lots or parcels.
b. In new or substantially improved manufactured home parks or subdivisions.
c. In expansions to existing manufactured home parks or subdivisions, or on a site in an existing manufactured home park or subdivision where a manufactured home has incurred "substantial damage" as the result of a flood, must have the lowest floor, including basement, elevated to the flood protection elevation.
2. Manufactured homes placed or substantially improved in an existing manufactured home park or subdivision may be elevated so that either:
a. The lowest floor of the manufactured home is elevated to the flood protection elevation or one foot (1') above the level of the base flood elevation, whichever is higher.
b. The manufactured home chassis is elevated and supported by reinforced piers (or other foundation elements of at least an equivalent strength) of no less than thirty six inches (36") above the highest adjacent grade.
3. Manufactured homes shall be anchored to prevent flotation, collapse, or lateral movement. Methods of anchoring may include, but are not limited to, use of over the top or frame ties to ground anchors. This standard shall be in addition to, and consistent with, applicable state requirements.
4. Manufactured homes placed on solid perimeter walls shall meet the flood vent requirements in subsection B4 of this section.
D. Accessory Structures: Relief from the elevation or dry floodproofing standards may be granted for an accessory structure containing no more than three thousand (3,000) square feet. Such a structure must meet the following standards:
1. It shall not be used for human habitation;
2. It shall be constructed of flood resistant materials;
3. It shall be constructed and placed on the lot to offer the minimum resistance to the flow of floodwaters;
4. It shall be firmly anchored to prevent flotation;
5. Services such as electrical and heating equipment shall be elevated or floodproofed to or above the flood protection elevation;
6. It shall meet the opening requirements of subsection B4 of this section.
E. Recreational Vehicle Standards: In all areas of special flood hazard, recreational vehicles must either:
1. Be on the site for fewer than one hundred eighty (180) consecutive days;
2. 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 structures or addition; or
3. The recreational vehicle must meet all the requirements for "new construction", including the anchoring and elevation requirements.
F. Floodway Standards: The following provisions shall apply in a floodway:
1. A project in the regulatory floodway must undergo an encroachment review to determine its effect on flood flows. An encroachment analysis must include:
a. Determination and documentation that the filling, grading or construction of a structure will not obstruct flood flows and will not cause an increase in flood heights upstream or adjacent to the project site;
b. Determination and documentation that grading, excavation, channel improvements, bridge and culvert replacements that remove an obstruction, do not cause increases in downstream flood flows;
c. Certification and documentation by a licensed professional engineer that the project will not result in a rise in flood heights;
d. The administrator may make the encroachment determination for minor projects, such as projects that do not increase the natural grade (e.g., paving a driveway or parking lot at existing grade, open fences and small isolated obstructions such as a mailbox or telephone pole).
2. Upon demonstrating that there are no alternatives, the applicant may propose an encroachment in the floodway that will cause an increase in the base flood elevation in excess of the allowable level provided that the applicant obtain a conditional letter of map revision from FEMA before the development can be approved and permitted.
G. Standards For Zones With Base Flood Elevations: In special flood hazard areas designated A1-30, AE, AH, A (with estimated BFE), the following provisions are required:
1. New Residential Construction And Substantial Improvements:
a. Where base flood elevation data are available, new construction or substantial improvement of any residential structure or manufactured home shall have the lowest floor, including basement, constructed at or above the community's flood protection elevation.
b. If solid foundation perimeter walls are used to elevate a structure, openings sufficient to facilitate the unimpeded movement of floodwaters shall be provided in accordance with the construction standards in subsection B4 of this section.
2. Nonresidential Construction: New construction or the substantial improvement of any nonresidential structure located in zones A1-30, AE, or AH must be floodproofed if the new construction or improvement is not elevated. The structure and attendant utility and sanitary facilities, must be designed to be watertight to the flood protection elevation or to one foot (1') above the base flood elevation, whichever is higher, with walls substantially impermeable to the passage of water, and structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy. A licensed professional engineer or architect must certify that the design and methods of construction are in accordance with accepted standards of practice for meeting these provisions, and shall provide certification to the administrator.
3. Places Where Floodway Not Determined: Where the floodway has not been determined, no new construction, substantial improvements, or other development (including fill) shall be permitted in zones A1-30 and AE on the effective 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 foot (1') at any point within the community. Applicants of proposed projects that increase the base flood elevation more than one foot (1') are required to obtain and submit to the floodplain administrator, a conditional letter of map revision (CLOMR) preconstruction.
4. Postconstruction Application: Postconstruction, the applicant must apply to FEMA for a letter of map revision for changes to the flood hazard map proposed in the CLOMR.
5. Drainage Paths: In AH zones, drainage paths shall be provided to guide floodwater around and away from proposed and existing structures.
H. Standards For Zones Without Base Flood Elevations And/Or Floodway (A Zones): These standards apply in special flood hazard areas where streams exist but no base flood elevation data have been provided (A zones), or where base flood data have been provided but a floodway has not been delineated.
1. When base flood elevation or floodway data have not been identified by FEMA in a flood insurance study and/or flood insurance rate maps, then the floodplain administrator shall obtain, review, and reasonably utilize scientific or historic base flood elevation and floodway data available from a federal, state, or other source, in order to administer this chapter. If data are not available from any source, only then provisions of subsections H2 and H3 of this section shall apply.
a. Where the floodplain administrator has obtained base flood elevation data, applicants of proposed projects that increase the base flood elevation more than one foot (1') shall obtain a conditional letter of map revision preconstruction and a letter of map revision postconstruction.
2. No encroachments, including structures or fill, shall be located within an area equal to the width of the stream or fifty feet (50'), whichever is greater, measured from the ordinary high water mark, unless certification by a licensed professional engineer documents that the encroachment will not result in any increase in flood levels during the base flood.
3. In special flood hazard areas without base flood elevation data, new construction and substantial improvements of existing structures shall have the lowest floor of the lowest enclosed area (including basement or crawl space) elevated no less than two feet (2') above the highest adjacent grade at the building site. Openings sufficient to facilitate the unimpeded movement of floodwaters shall be provided in accordance with the construction standards in subsections B and C of this section.
I. Standards For Areas Of Shallow Flooding (AO Zones): Shallow flooding areas designated AO zones, are areas of special flood hazard that have base flood depths of one to three feet (3'), with no clearly defined channel. The following provisions apply:
1. All new construction and substantial improvements of residential and nonresidential structures shall have the lowest floor, including basement, elevated above the adjacent grade at least as high as the flood depth number specified in feet on the flood insurance rate map (FIRM). If no flood depth number is specified, the lowest floor, including basement, shall be elevated at least two feet (2') above the highest adjacent grade. Openings sufficient to facilitate the unimpeded movement of floodwaters shall be provided in accordance with the construction standards in subsection B4 of this section.
2. New construction or the substantial improvement of a nonresidential structure may be floodproofed in lieu of elevation. The structure and attendant utility and sanitary facilities must be designed to be watertight to the specified base flood level or at least two feet (2') above highest adjacent grade, with walls substantially impermeable to the passage of water, and structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy. A registered professional engineer or architect shall certify that the design and methods of construction are in accordance with accepted standards of practice for meeting these provisions, and shall provide certification to the floodplain administrator.
3. Drainage paths shall be provided to guide floodwater around and away from all proposed and existing structures.
J. Alteration Of A Watercourse: A watercourse is considered altered when any change occurs within its banks.
1. The bankfull flood carrying capacity of the altered or relocated portion of the watercourse shall not be diminished. Prior to issuance of a floodplain development permit, the applicant must submit a description of the extent to which any watercourse will be altered or relocated as a result of the proposed development and submit certification by a registered professional engineer that the bankfull flood carrying capacity of the watercourse will not be diminished.
2. Adjacent communities, the U.S. army corps of engineers and the Idaho department of water resources stream channel alteration program must be notified prior to any alteration or relocation of a water source. Evidence of notification must be submitted to the floodplain administrator and to the federal emergency management agency.
3. The applicant shall be responsible for providing the necessary maintenance for the altered or relocated portion of the watercourse so that the flood carrying capacity will not be diminished.
4. The applicant shall meet the requirements to submit technical data in subsections K1 and K2 of this section when an alteration of a watercourse results in the relocation or elimination of the special flood hazard area, including the placement of culverts.
K. Requirement To Submit New Technical Data:
1. For all development proposals that impact floodway delineations or base flood elevations, the community shall ensure that technical data reflecting such changes be submitted to FEMA within six (6) months of the date such information becomes available. These development proposals include:
a. Floodway encroachments that increase or decrease base flood elevations or alter floodway boundaries;
b. Fill sites to be used for the placement of proposed structures where the applicant desires to remove the site from the special flood hazard area in accordance with subsection A3 of this section;
c. Alteration of watercourses that result in a relocation or elimination of the special flood hazard area, including the placement of culverts;
d. Subdivision or large scale development proposals requiring establishment of base flood elevations according to subsection A3 of this section.
2. It is the responsibility of the applicant to have technical data prepared in a format required for a conditional letter of map revision or letter of map revision and submitted to FEMA. Submittal and processing fees for these map revisions shall be the responsibility of the applicant. (Ord. 2129, 3-3-2015)