Each building type is based on their fire-resistance rating. The more fire-resistant the larger and taller a project may be. The International Building Code spells out these types. Below are the basic characteristics of each type.
Type I (IA and IB)- The most stringent of building types when it comes to fire-resistance rating requirements, a Type I building, including its roof, must be composed of noncombustible materials like concrete and steel.
Type II (IIA and IIB)- With noncombustible steel or concrete structural framework, walls, and floors, Type II is similar to Type I, but requires lower fire-resistance ratings. It’s a very commonly used construction type and Type IIB has no fire resistance requirements for any of the building elements, provided that there is adequate fire separation distance, as laid out in Table 602.
Type III- Also known as a brick-and-joist structure, a Type III building has exterior walls built out of noncombustible materials (like masonry or concrete) and the floors, roof, and structural framework can be made of any material permitted by the code (like wood).
Type IV- Buildings constructed out of heavy timber (HT) are designated Type IV. With noncombustible exterior walls and interior elements made out of solid or laminated wood, a Type IV building cannot have a wood column any less than 8 inches thick or a wood girder any less than 6 inches thick. While similar to a Type III, Type IV instead relies on the fire-resistant nature of the large dimension lumber in place of a prescribed fire-resistance rating.
Type V- The most combustible of the five building types and the only one that allows for combustible exterior walls, Type V buildings allow both the exterior walls and interior framing to be wood. It’s a common construction method for single-family homes.
Building construction type, when combined with occupancy, is an important factor for many code requirements. It is an important detail that must be considered during the design phase of any construction project. Particularly when determining the ultimate use and goals for the project.