The volume of a space within a building or fire compartment. This volume does not include the walls of protected elevator shafts, escape stairwells, and other spaces (e.g., restrooms and storage rooms) enclosed by walls with a fire resistance of not less than 60 minutes, and the passages through walls are protected by type 2 fire doors fitted with self-closing devices. The volume scale is calculated using the following dimensions:

a) The plan dimensions are taken as the distance between the finished inner surfaces of the enclosing walls, or on all sides without enclosing walls, it is taken to a vertical plane extending to the outer edge of the top of the floor;

b) The height is taken as the distance from the top surface of the floor below to the bottom surface of the floor above the space;

c) For a building or fire compartment extending to the roof, it is taken as the distance to the bottom surface of the roof or the bottom surface of the ceiling of the highest floor in the fire compartment, including the space occupied by all walls, or unprotected vertical shafts, ducts, or structures within the space under consideration.