International Building Code Section 413

International Building Code 413.1

General. High-piled stock or rack storage in any occupancy
group shall comply with the International Fire Code.

International Building Code 413.2

Attic, under-floor and concealed spaces. Attic,
under-floor and concealed spaces used for storage of combustible
materials shall be protected on the storage side as required
for 1-hour fire-resistance-rated construction. Openings shall
be protected by assemblies that are self-closing and are of
noncombustible construction or solid wood core not less than
13/4 inch (45 mm) in thickness.
1. Areas protected by approved automatic sprinkler systems.
2. Group R-3 and U occupancies.