24.321.308    EXTERIOR AREAS

(1) In structures where the window to exterior wall area exceeds 20 percent (i.e., more than 20 percent of all exterior wall areas is comprised of exterior windows or window walls), the exterior windows, window walls, glazed doors, glazing within exterior doors, and skylights shall be tempered glass, multilayered glazed panels, glass block, or have a fire protection rating of not less than 20 minutes.

(2) Exterior doors shall be of approved noncombustible construction and materials, solid core wood not less than 1 3/4 inches thick, or have a fire protection rating of not less than 20 minutes. Vehicle access doors shall be constructed of ignition-resistant building materials.

(3) Exterior walls of buildings or structures shall extend from the top of the foundation to the underside of the roof sheathing and shall be constructed with one of the following methods:

(a) materials approved for a minimum of one-hour fire-resistance-rated construction on the exterior side;

(b) noncombustible materials;

(c) heavy timber or log wall construction;

(d) wood that is labeled for exterior use and is fire-retardant-treated on the exterior side; or

(e) materials that are ignition-resistant on the exterior side.

(4) If a structure is not located in a designated WUI, this rule does not apply.

History: 50-60-901, MCA; IMP, 76-3-504, MCA; NEW, 2011 MAR p. 319, Eff. 2/25/11.