The primary characteristic of Class B buildings is the reinforced concrete frame in which the columns and beams can be either formed or precast concrete. They may be mechanically stressed. Class B buildings are fire-resistant structures.
Floors and roofs in Class B structures are formed or precast concrete slabs. The exterior walls, generally, are masonry or reinforced concrete curtain walls or any of the many types of wall panels of concrete, metal, glass or stone. In some Class B buildings the walls may be partially loadbearing. Interior partitions are often masonry, reinforced concrete or gypsum block. Many lightweight and movable partitions are used where structural walls are not needed.
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 concrete. 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 Fire Resistive or Two-Four-hour construction.