All of the codes rely on independent, third-party standards as the basis for materials or building assemblies to demonstrate code compliance. For example, the American Society of Testing Materials (ASTM) and Underwriters Laboratory (UL) each maintain their own well-recognized library of testing protocols. These standards apply to many different building situations and establish the accepted means for evaluating things like fire-resistance ratings among many others. Using these testing standards, manufacturers can have their products tested by independent labs and have the results reported. The codes identify the testing results required to show compliance.

Relatedly, manufacturers can submit their tested products for review to the ICC Evaluation Service (ICC-ES, a subsidiary of the International Code Council). Once reviewed and evaluated, an ICC-ES Evaluation Report can be generated which describes the details and conditions in which a particular product is found to be code-compliant and therefore consistent with safety standards.

Types of Construction

When designing any building, one of the first things that needs to be identified is the type of construction to be used as defined by the codes. Architects can choose which type to design and construct, but each choice comes with some requirements and restrictions. In some cases, the size (area) or height of the building will determine which Type(s) are acceptable for fire safety, particularly in site locations with local fire zone requirements. Chapter 6 of the 2021 IBC defines the Types, summarized as follows:

• Type I construction requires noncombustible materials for the primary building elements with two levels of fire resistance identified:
• Type IA – The primary structural frame and exterior and interior bearing walls must be noncombustible with 3 hours of tested fire resistance, which usually means masonry and concrete are used. Floor construction only requires 2 hours of fire-resistance rating, and roof construction requires only 1-1/2 hours of fire-resistance rating. If steel construction is used, it usually means that the steel structure is protected with spray-on fire protection products.
• Type IB – The difference between IA and IB is that IB allows slightly lower fire-resistance ratings of noncombustible assemblies with the primary structural frame and bearing walls rated at 2 hours, floor construction at 2 hours, and roof construction at 1 hour.

• Type II also needs to be constructed with noncombustible materials but they have lower fire resistance requirements than Type I.
• Type IIA includes the primary structural frame, bearing walls, and the floor and roof construction at only 1-hour rating.
• Type IIB does not require any fire-resistance rating for the structure, walls, floor, or roof; just noncombustible materials.

Exceptions to the above are identified in Section 603 of the IBC which addresses the use of permitted combustible products in Types I and II Construction, including the selective use of fire-retardant-treated wood for certain non-structural elements or secondary structural elements.

• Type III construction requires noncombustible materials only on the exterior walls while interior building elements can be of any code-permitted material, whether or not it is combustible. Fire-retardant-treated wood framing and sheathing are specifically identified and permitted within exterior wall assemblies with a 2-hour rating or less.
• Type IIIA includes a 2-hour rating for exterior walls, but only a 1-hour rating for the primary structural frame, interior bearing walls, and the floor and roof construction.
• Type IIIB only requires a 2-hour rating for exterior walls and no other fire rating for the structure, interior walls, floor, or roof.
• Type IIIB only requires a 2-hour rating for exterior walls and no other fire rating for the structure, interior walls, floor, or roof.
• Type IV construction includes mass timber elements combined with noncombustible materials based on the requirements of the sub-types. Note that the 2021 version of the IBC requires noncombustible material to be applied over exposed mass timber and some surfaces, “designed to increase the fire-resistance rating and delay the combustion of mass timber” in Types IV-A, IV-B, and IV-C construction, but not in Type IV-HT.
• Type IV-A – The primary structural frame and exterior and interior bearing walls must achieve 3 hours of tested fire resistance. That usually means masonry or concrete exterior walls and protected frame and interior bearing walls. The floor construction only requires 2 hours of fire-resistance rating, and the roof construction requires only 1-1/2 hours of fire-resistance rating.
• Type IV-B – The primary structural frame and all exterior and interior bearing walls need to be rated at 2 hours, floor construction at 2 hours, and roof construction at 1 hour.
• Type IV-C – has the same fire-resistance ratings as Type IV-B but has fewer requirements for noncombustible coverings or coatings.
• Type IV-HT construction calls for exterior walls to be of noncombustible materials while interior building elements are permitted to be of heavy timber construction including solid wood, laminated heavy timber, or structural composite lumber. Heavy timber must meet minimum size requirements such that it will char during a fire but retain its strength for at least the rated amount of time required. FRTW framing and sheathing assemblies are permitted in exterior walls with a 2-hour fire rating or less. Cross-laminated timber (CLT) is also permitted in exterior walls provided it is protected by FRTW sheathing, gypsum board, or a noncombustible material.
• Type V construction allows for the structural elements, exterior walls, and interior walls to be of any materials permitted by the code. Type V is commonly associated with conventional wood-framed residential construction.
• Type V-A requires buildings to have a 1-hour fire-resistance rating for the structural frame, exterior and interior bearing walls, floor construction, and roof construction, but not interior non-load bearing walls.
• Type V-B places no requirements for any fire ratings on any building elements.

The design professional of record can choose which construction type to use on any particular building provided that it is coordinated with the other requirements throughout the code for the selected type of construction. Those other requirements include building occupancy, fire protection requirements, size limitations, height restrictions, and other factors.