The main difference between Type I-A and Type B is that the Type I-B building has exterior walls and a structural frame that only has to withstand fire for two hours, instead of the three hours of Type I-A. “Each type of construction is further described as “" A "” or “" B "”.” Suffice it to say that a designation of type B is basic and that type A is improved. For the purpose of this overview, we will begin by describing the less stringent construction of Type V and work our way up to Type I. With Type A, ratings range from 1 to 3 hours, and sometimes sprinklers may be replaced by rating.
The type of construction you select is important because it tells you how big and tall you can build a building for occupancy. The objectives of Type III construction are to contain any fire within the exterior walls of the building and to mitigate the spread of fire to adjacent buildings. The sub-designations of both types of construction (I-A, I-B, II-A & II-B) will determine the extent to which non-combustible elements require fire ratings. This type of construction is commonly referred to as heavy wood construction, since it relies on the thickness and mass of the heavy wood elements to provide a degree of fire resistance.
Type III construction requires non-combustible exterior walls and allows for combustible interior construction. On the other hand, when a building is incorrectly classified into an overly lenient type of construction, it will not be constructed in a manner that takes into account the relative risks associated with its size or function. The main purpose of categorizing various types of construction is to establish a basic level of safety for occupants in the event of a fire. A Type I building: A building (the “improved Type I construction”) adds even more layers of protection and is necessary for buildings such as skyscrapers, where even the height is unlimited (in theory).
Many code requirements applicable to a building, such as the height and area allowed (see chapter), depend on the type of construction. In volume one of the National Building Code (NCC) (Section C — Fire Resistance), the “type of construction” generally determines how much a building is expected to be fire resistant (including all building elements, structural members, and non-load-bearing components). The exterior walls of Type III construction are constructed of bricks, masonry, concrete blocks, prefabricated panels, or other non-combustible materials. Hospitals or jails where occupants are confined and unable to leave on their own may require stricter types of construction, even as single-story buildings.
The many nuances of a building's use and size requirements can complicate things and create confusion as to what type of construction is best suited. To answer this, it is important to understand what the term “type of construction” means. Construction materials and practices used in Type I construction provide the highest level of fire protection.