Chapter Six of the International Building Code (IBC) defines five major Types of Construction – Type I through Type V. Among other parameters, the Type of construction determines when and how combustible building materials may be used. These requirements are essential for the designer and the builder to understand and follow to ensure that a building is safe and code-compliant.
We must keep two definitions in mind when considering construction Types: combustible and non-combustible materials. The IBC defines non-combustible materials as materials that, under anticipated conditions, will not ignite or burn when subjected to fire or heat. Materials that pass ASTM E136 are considered non-combustible materials.
The table below lists the construction Types from most restrictive (non-combustible) to least restrictive (combustible). Typical phrases used to describe each Type are also provided in the table, although these should not be confused as limitations on the building materials permitted in each Type.
International Building Code Construction Types
While a general description of each Type is helpful in gaining a basic understanding of their use, it is essential to know the IBC contains many specific and detailed exceptions to many requirements. Below we provide a brief, basic description of each Type.
Type I Construction
Type I construction contains the most restrictive fire-resistive standards and typically applies to buildings over 75 feet tall. All structural materials used in Type I construction must be non-combustible; in the prescriptive code, walls, floors, and roofs in Type I construction are typically constructed with reinforced concrete and protected steel. The structural frame and exterior walls must have fire ratings of at least three hours and floors and ceilings of at least two hours.
Type II Construction
While similar in restrictions to Type I construction, buildings in Type II construction are not over 75 feet tall. They typically contain non-combustible columns, floors, partitions, roofs, and walls. Type II construction will typically contain a fire suppression system.
Section 603.1 of the IBC allows for the use of combustible materials in buildings of Type I or II construction in many applications. For example, specific instances of fire-retardant-treated wood, thermal and acoustical insulation, foam plastics, and roof coverings are permitted.
Type III Construction
The exterior walls of Type III construction use non-combustible materials, while the interior building elements may be any material permitted by code. The IBC permits fire-retardant-treated wood framing and sheathing that comply with Section 2303.2 for exterior wall assemblies of a 2-hour rating or less.
Fire-retardant-treated wood in Section 2303.2 of the IBC is permitted in assemblies when tested in accordance with ASTM E84 or UL 723 and has a listed flame spread index of 25 or less. ASTM E84 or UL 723 test will continue for a 20-minute period, and the flame front should not progress more than 10.5 feet beyond the centerline of the burners at any time during the test.
Type IV Construction
Type IV construction was the most heavily revised area of Chapter 6 in the 2021 IBC. Prescriptively, Type IV construction consists of mass timber or non-combustible materials. Except where otherwise specified, combustible concealed spaces are not permitted in Type IV construction. Type IV construction has four sub-types (IV-A, IV-B, IV-C, and IV-HT), each with its own requirements.
Type V Construction
The least restrictive category, Type V construction, allows any materials that the IBC permits. Single-family homes are typically part of this category and give the most freedom to designers and builders.
Understanding the requirements for each Type of construction is essential for designers, builders, and material suppliers. When all parties are aligned on the expectations, project timelines and budgets are easier to manage, and it is less likely the local authority having jurisdiction will need to issue a corrective action for the building.
Sources:
National Fire Protection Association. “Types of Construction and Material Combustibility.” NFPA, https://www.nfpa.org/News-and-Research/Publications-and-media/Blogs-Landing-Page/NFPA-Today/Blog-Posts/2021/02/19/Construction-Types-and-Material-Combustibility?icid=W467. Accessed 07/06/2022.
New England Institute of Technology. “What are the Different Types of Construction?.” NEIT, https://www.neit.edu/blog/what-are-the-different-types-of-construction. Accessed 07/06/2022.
