Buildings are classified by type of construction--literally how the building is constructed as dictated by the International Building Code. The classification takes into account a very important aspect: how well the building resists fire. As might be expected, thanks to the many materials from which a building is made, there is a wide range of classes within this classification.
Type I-A and B
The Type I-A building construction produces a building that has exterior walls and a structural frame that are able to withstand fire up to three hours. Both the floor and the ceiling need to resist fire for two hours, while the roof should resist fire up to one and a half hours. Buildings that fall within this type are often high-rise structures. The main difference between the Type I-A and B is that the Type I-B building has exterior walls and a structural frame that only has to resist fire for two hours, rather than the three hours of the Type I-A.
Type II-A and B
The Type II-A building is considered one that is protected and non-combustible, and often includes newer schools. These buildings have exterior walls, structural frames and a ceiling, roof and floor that should last up to one hour. The main difference between the Type II-A and Type II-B building is that while the II-B building is made from non-combustible materials, it has no fire resistance to speak of. Most commercial buildings fall within this construction type.
Type III-A and B
The Type III-A building construction includes buildings that have walls of brick or even block, and can have wooden roofs. For these buildings, the exterior walls should last up to two hours while the rest of the building should last up to an hour. Warehouses that have brick or block exterior walls fall into the Type III-B category, and can last up to two hours; the rest of the building has no fire protection whatsoever.
Type IV actually stands alone in this type of building construction. This category includes what is termed heavy timber, because each of the timbers used must be at least 8 inches around or more. This type of construction is often used for mills, and their exterior walls should last for two hours while the structural frame should last for one. The floor, ceiling and roof have no rating, but each should be constructed of the heavy timber.
Type V-A and B
This is the last in the types of building construction. Type V-A buildings are constructed of wood that is considered protected in that the exterior walls, the structural frame, roof, floor and ceiling should all last for up to an hour. The caveat is that there needs to be no exposed wood inside the structure. Most of the buildings that fall into this category are apartment buildings that have been built more recently. Type V-B includes most wooden houses that are single-family as well as garages. These buildings are considered unprotected, as there is often exposed wood inside the structures. They also have no fire protection.