Subsection R302.7.1 is hereby added to the International Residential Code for One- and Two-Family Dwellings and shall read as follows:

R302.7.1 Under-Stairway Protection. Under-stair surfaces of stairways shall be protected with 1/2-inch gypsum board.

EXCEPTIONS:

1. Exterior stairways.

2. Stairways of noncombustible materials.

3. Decorative and open stairways where approved by the building official.