36.15.702    FLOOD PROOFING FOR RESIDENTIAL, COMMERCIAL, AND INDUSTRIAL STRUCTURES

(1) The new construction, substantial improvement, and alteration of residential structures shall meet the following conditions:

(a) Residential structures shall be constructed on suitable fill with a permanent foundation such that the lowest floor (including basement) level is 2 or more feet above the base flood elevation. The suitable fill shall be at a level no lower than the base flood elevation extending 15 feet at that elevation beyond the structure in all directions. Where existing streets, utilities, lot dimensions, or additions onto existing structures, make strict compliance with this provision impossible, the permit issuing authority may authorize a lesser amount of fill or alternative flood proofing measures. Alternative flood proofing measures must, at a minimum, meet the conditions of ARM 36.15.702 and ARM 36.15.901 through 36.15.903.

(i) The new placement of manufactured and mobile homes must be elevated on fill with a permanent foundation as prescribed for residential structures.

(ii) Replacement manufactured and mobile homes in an existing mobile home park or subdivision may, instead of using suitable fill, be elevated on a concrete or mortared block foundation, or other suitable permanent foundation, and anchored to prevent flotation or downstream movement.

(2) The new construction, substantial improvement, and alteration of commercial and industrial structures shall be elevated on fill as prescribed for residential structures in ARM 36.15.702(1) or flood proofed to a level no lower than 2 feet above the base flood elevation. Flood proofing shall be accomplished in accordance with ARM 36.15.901 through 36.15.903 and shall further include the following:

(a) If the structure is designed to allow internal flooding of the lowest floor, use of the floor shall be limited to such uses as parking, loading areas, and storage of equipment or materials not appreciably affected by flood water. Further, the floors and walls shall be designed and constructed of materials resistant to flooding up to an elevation of 2 or more feet above the elevation of the base flood. Structures designed to allow internal flooding shall be designed to equalize hydrostatic flood forces on exterior walls by allowing for the exit and entry of flood waters.

(b) Structures whose lowest floors are used for purposes other than parking, loading or storage of materials resistant to flooding shall be flood proofed up to an elevation no lower than 2 feet above the elevation of the base flood. Flood proofing shall include impermeable membranes or materials for floors and walls and watertight enclosures for all windows, doors, and other openings. These structures shall be designed to withstand the hydrostatic pressures and hydrodynamic forces resulting from the base flood.

(c) The new construction, substantial improvement and alteration of commercial or industrial structures floodproofed according to these requirements must be designed and flood proofing measures certified as adequate by a registered professional engineer or architect.

History: Sec. 76-5-208, MCA; IMP, Sec. 76-5-404 through 76-5-406, MCA: NEW, Eff. 9/4/74; AMD, 1989 MAR p. 1665, Eff. 10/27/89.