Sec.11-8-7. Roof

(a) Structure-supported vaults. In structure-supported vaults, the roof or floor of the fire-resistive buildings may served for the roof of the vault, if it is of noncombustible construction throughout and complies with the following requirements: (1) The roof of the vault shall be of reinforced concrete on reinforced concrete or protected steel supports. (2) The roof of the vault shall be at least six inches thick; if it is subject to unusual impact or exposed to undue fire hazard from outside the vault, it shall have a thickness equivalent to that required for the walls. (3) All interior structural steel shall be protected with at least two inches of fireproofing. (4) Roofs of vaults shall not be pierced for any purpose.

(b) Ground-supported vaults. In ground-supported vaults, the requirements in subdivisions (1) to (4), inclusive, of subsection (a) shall apply. In addition, in a nonfire-resistive building, the roofs of vaults shall be entirely independent of the wall, floor, ceiling, columns, piers or roof construction of the building.