The primary feature of Class A buildings is the fireproofed structural steel frame, which may be welded, bolted or riveted together. The fireproofing may be masonry, poured concrete, plaster, sprayed fiber or any other method which gives a high fire-resistance rating.
Floor and roof in Class A structures are normally reinforced concrete on steel decking or formed slabs resting on the frame or poured to become integral with it. They may also be composed of prefabricated panels and may be mechanically stressed.
Exterior walls are curtain walls of masonry, concrete, steel studs and stucco, or one of the many types of panels of metal, glass, masonry or concrete. Interior partitions frequently are of masonry or gypsum block, although many movable and lightweight steel partitions are used.
Included in this class are Uniform, Basic and Standard Building Code construction, Types I and II (noncombustible) and ISO Classes 5 and 6, if the framing is protected steel. ISO Class 5 and 6 buildings with load-bearing walls and no interior framing and most low-rise buildings should be classified as Class C for pricing purposes. This class is also referred to as Modified Fire Resistive or Two-Four-hour construction.