(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
(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
(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.