The floors and roofs of all school buildings shall be so designed and constructed as to sustain safely with a safety factor of at least four the following superimposed or live loads in addition to the weight of the construction or dead load:

Classrooms ........................................... 60 pounds per sq. ft.

Corridors ............................................ 80 pounds per sq. ft.

Auditorium with fixed seats .......................... 100 pounds per sq. ft.

Auditorium with movable seats ........................ 125 pounds per sq. ft.

Gymnasiums ........................................... 150 pounds per sq. ft.

Roofs ................................................ 30 pounds per sq. ft.