Penthouses or Roof Structures. Penthouses or roof structures for the housing of elevators, stairways, tanks, ventilating fans, television aerials or similar equipment required to operate and maintain the building; fire or parapet walls, skylights, towers, roof signs, flagpoles, chimneys, smokestacks, wireless masts and similar structures may be erected above the height limits prescribed by the height and area regulations, but no penthouse or roof structure, or any other space above the height limit prescribed for the zone in which the building is located shall be allowed for the purpose of providing additional floor space.