In all cases of special flood hazards where base flood elevation (BFE) data has been provided as set forth in section 10-1-6 of this chapter, the provisions of this section shall be required:
A. Residential Construction:
1. Connection to a central sewage treatment system shall be required. This requirement may be waived by the city council if the Central district health department recommends approval of an alternate method of sewage treatment and disposal. Residential development within the floodplain may be clustered (through approval of a PUD) to facilitate the economics of the sewage infrastructure.
2. New construction and substantial improvement of any residential structure (including manufactured homes) shall have a finish floor elevated no lower than the flood protection elevation, as defined in section 10-1-5, and the lowest floor, including basement and crawl space, shall be elevated to a minimum of one foot (1') above the base flood elevation.
3. 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 either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria:
a. A minimum of two (2) openings on different sides 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 total net area of all flood openings must be at least one (1) square inch for each square foot of enclosed area subject to flooding.
c. If a building has more than one (1) enclosed area, each enclosed area must have flood openings to allow floodwaters to automatically enter and exit.
d. The bottom of all required flood openings shall be no higher than one foot (1') above the interior or exterior adjacent grade.
e. Flood openings may be equipped with screens, louvers, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.
f. Enclosures made of flexible skirting are not considered enclosures for regulatory purposes, and, therefore, do not require flood openings. Masonry or wood underpinning, regardless of structural status, is considered an enclosure and requires flood openings as outlined above.
4. Additions/Improvements:
a. Additions and/or improvements to pre-FIRM structures when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(1) Not a substantial improvement, the addition and/or improvements must be designed to minimize flood damages and must not be any more non-conforming than the existing structure; or
(2) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
b. Additions to post-FIRM structures that are a substantial improvement with no modifications to the existing structure other than a standard door in the common wall shall require only the addition to comply with the standards for new construction.
c. Additions and/or improvements to post-FIRM structures when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(1) Not a substantial improvement, the addition and/or improvements only must comply with the standards for new construction; or
(2) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
d. Any combination of repair, reconstruction, rehabilitation, addition, or improvement of a building or structure taking place during a ten (10) year period, the cumulative cost of which equals or exceeds forty percent (40%) of the market value of the structure before the improvement or repair is started, must comply with the standards for new construction. For each building or structure, the ten (10) year period begins on the date of the first improvement or repair of that building or structure subsequent to the effective date of this chapter. If the structure has sustained substantial damage, any repairs are considered substantial improvement regardless of the actual repair work performed. The requirement does not, however, include either:
(1) Any project for improvement of a building required to correct existing health, sanitary, or safety code violations identified by the building official and that are the minimum necessary to assume safe living conditions; or
(2) Any alteration of a historic structure provided that the alteration will not preclude the structure's continued designation as a historic structure.
B. Nonresidential Construction: New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall either have the lowest floor elevated to no lower than the flood protection elevation, as defined in section 10-1-5; or together with attendant utility and sanitary facilities, shall:
1. Be floodproofed to a point two feet (2') above the base flood elevation so that 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; and
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 as set forth in subsection 10-1-9B of this chapter.
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 (1') below the floodproofed level (e.g., a building constructed to the base flood level will be rated as 1 foot below that level).
C. Manufactured Homes:
1. New and replacement manufactured homes shall be elevated so that the lowest floor of the manufactured home is no lower than the flood protection elevation, as defined in section 10-1-5.
2. Manufactured homes shall be securely anchored to an adequately anchored foundation to resist flotation, collapse, and lateral movement, either by certified engineered foundation system, or in accordance with the most current edition of the Idaho division of building safety's "Idaho Manufactured Home Installation Standard" in accordance with Idaho Code, section 44-2201(2). Additionally, when the elevation would be met by an elevation of the chassis thirty six (36) inches or less above the grade at the site, the chassis shall be supported by reinforced piers or engineered foundation. When the elevation of the chassis is above thirty six (36) inches in height, an engineering certification is required.
3. All enclosures or skirting below the lowest floor shall meet the requirements of section 10-1-8-6A3.
4. An evacuation plan must be developed for evacuation of all residents of all new, substantially improved, or substantially damaged manufactured home parks or subdivisions located within flood prone areas. This plan shall be filed with and approved by the floodplain administrator and the local emergency management coordinator.
D. Recreational Vehicles: Recreational vehicles shall be either: In all areas of special flood hazard (ASFH), recreational vehicles must be either:
1. Temporary Placement: Be on site for fewer than one hundred eighty (180) consecutive days and be fully licensed and ready for highway use (a recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick disconnect type utilities, and has no permanently attached additions); or
2. Permanent Placement: Recreational vehicles that do not meet the limitations of temporary placement shall meet all the requirements for new construction, as set forth in section 10-1-8-2.
E. Temporary Non-Residential Structures: Prior to the issuance of a floodplain development permit for a temporary structure, the applicant must submit to the floodplain administrator a plan for the removal of such structure(s) in the event of a flash flood or other type of flood warning notification. The following information shall be submitted in writing to the floodplain administrator for review and written approval:
1. A specified time period for which the temporary use will be permitted. Time specified may not exceed six (6) months, renewable up to one (1) year;
2. The name, address, and phone number of the individual responsible for the removal of the temporary structure;
3. The time frame prior to the event at which a structure will be removed (for example, immediately upon flood warning notification);
4. A copy of the contract or other suitable instrument with the entity responsible for physical removal of the structure; and
5. Designation, accompanied by documentation, of a location outside the special flood hazard area, to which the temporary structure will be moved.
F. Accessory Structures: When accessory structures (sheds, detached garages, and the like) are to be placed within a special flood hazard area, elevation or floodproofing certifications are required for all accessory structures (except as exempted below) in accordance with section 10-1-8-2B and/or J2 and the following criteria shall be met:
1. Accessory structures shall not be used for human habitation (including working, sleeping, living, cooking, or restroom areas);
2. Accessory structures shall not be temperature-controlled;
3. Accessory structures shall be designed to have low flood damage potential;
4. Accessory structures shall be constructed and placed on the building site so as to offer the minimum resistance to the flow of floodwaters;
5. Accessory structures shall be firmly anchored in accordance with the provisions of section 10-1-8-3 of this chapter;
6. All service facilities, such as electrical, shall be installed in accordance with the provisions of section 10-1-8-2C of this chapter; and
7. Flood openings to facilitate automatic equalization of hydrostatic flood forces shall be provided below flood protection elevation in conformance with the provisions of section 10-1-8-6A3 of this chapter.
An accessory structure with a footprint less than two hundred (200) square feet and is a minimal investment of three thousand dollars ($3,000.00) or less and satisfies the criteria outlined in divisions a. through g. above is not required to meet the certification requirements of elevation or floodproofing standards section 10-1-8-6B of this chapter.
G. Tanks: When gas and liquid storage tanks are to be placed within a special flood hazard area, the following criteria shall be met:
1. Underground tanks in flood hazard areas shall be anchored to prevent flotation, collapse, or lateral movement resulting from hydrodynamic and hydrostatic loads during conditions of the base flood, including the effects of buoyancy (assuming the tank is empty);
2. Elevated above-ground tanks, in flood hazard areas shall be attached to and elevated to or above the design flood elevation on a supporting structure that is designed to prevent flotation, collapse, or lateral movement during conditions of the base flood. Tank-supporting structures shall meet the foundation requirements of the applicable flood hazard area;
3. Not elevated above-ground tanks, that do not meet the elevation requirements of section 10-1-8-6B shall be permitted in flood hazard areas provided the tanks are anchored or otherwise designed and constructed to prevent flotation, collapse or lateral movement resulting from hydrodynamic and hydrostatic loads during conditions of the design flood, including the effects of buoyancy assuming the tank is empty and the effects of flood-borne debris.
4. Tank inlets, fill openings, outlets and vents shall be:
a. At or above the flood protection elevation or fitted with covers designed to prevent the inflow of floodwater or outflow of the contents of the tanks during conditions of the base flood; and
b. Anchored to prevent lateral movement resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood.
H. Construction Of Below-Grade Crawlspace:
1. The interior grade of a crawlspace shall be one-foot (1') above the base flood elevation (BFE) and must not be more than two (2) feet below the exterior lowest adjacent grade (LAG).
2. 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 feet (4') at any point.
I. Other Development In Regulated Floodways:
1. Fences that have the potential to block the passage of floodwaters, such as stockade fences and wire mesh fences, in regulated floodways and flood fringe shall meet the limitations of section 10-1-8-7C.
2. Retaining walls, bulkheads, sidewalks, and driveways that involve the placement of fill in regulated floodways and flood fringe shall meet the limitations of section 10-1-8-7C.
3. Roads and watercourse crossings, including roads, bridges, culverts, low-water crossings, and similar means for vehicles or pedestrians to travel from one side of a watercourse to the other side, which encroach into regulated floodways and flood fringe, shall meet the limitations of section 10-1-8-7C.
4. Drilling water, oil, and/or gas wells including fuel storage tanks, apparatus, and any equipment at the site that encroach into regulated floodways and flood fringe shall meet the limitations of section 10-1-8-7C and M.
5. Docks, piers, boat ramps, marinas, moorings, decks, docking facilities, port facilities, shipbuilding, and ship repair facilities that encroach into regulated floodways and flood fringe shall meet the limitations of section 10-1-8-7C.
(Ord. 332, 2-23-1999; amd. Ord. 485, 7-24-2007; Ord. 700A, 3-11-2014; Ord. 815, 7-23-2019)
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