(1) All underfloor areas shall be enclosed to the ground in the same manner as required for exterior walls in ARM 24.321.308, unless such unenclosed areas are protected with either one-hour fire-resistance-rated construction or heavy timber construction or fire-retardant-treated wood to the underside of all exposed floors and all exposed structural columns, beams, and supporting walls.

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