315.2.4 Attic, under-floor and concealed spaces.
FC § 315.2.4
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 1.75 inches (44.5 mm) in thickness. Storage shall not be placed on exposed joists. Exceptions: 1. Areas protected throughout by sprinkler systems.
2.Group R-3 and Group U occupancies.
3.Groups S-1 and S-2 occupancies.
