Where an apron is provided, the
apron shall be not less than 8 inches (203 mm) above,
nor less than 24 inches (610 mm) below, grade. The
apron shall not terminate below the lower edge of the
siding material. The apron shall be constructed of an
approved nondecayable, water-resistant rodentproofing
material of required strength and shall be installed
around the entire perimeter of the building. Where constructed
of masonry or concrete materials, the apron
shall be not less than 4 inches (102 mm) in thickness.