When the type of construction of the building is used in the building code, the reference is to one of five categories of construction, based on the relative fire safety of each type. Currently, the classifications of construction types are ranked on the combustibility of the entire assembly, versus the fire-resistivity of the basic materials. Note that each type is not specific to a specific material. In actuality, concrete and steel may be used in any of the types of construction, but the use of wood is severely limited in construction types I and II.
Construction Types
- Type I (Non-Combustible Fire-Resistive Construction) – Examples include concrete columns, beams and floors; this type of construction has high assembly fire resistivity.
- Type II (Non-combustible) – Examples included steel columns, beams and deck/floors.
- Type III ("Hybrid" Non-Combustible / Combustible) – Examples include concrete tilt-up construction with wood glulam (subdiaphragm) roof.
- Type IV ("Heavy Timber") – Examples include 6x10 wood beams / 8x8 wood columns / cross-laminated timbers.
- Type V (Wood Frame Construction) – Examples include wood or metal stud construction; this type of construction has low assembly fire resistivity.
Type I and II
Type IA and IB - Non-combustible construction (i.e., typically steel or concrete) requiring high to moderate levels of fire protection. These structures are often reinforced concrete structures or steel structures with a high degree of fire-resistance detailing using either concrete encasement or spray applied fireproofing systems.
Type IIA and IIB - Non-combustible construction requiring either low (“one-hour”) or no fire-resistant construction. This type of construction is typically heavy steel construction using moment frames or brace frames as a lateral force resisting system. Interior partitions are typically framed from light-gauge metal studs. Spray applied fireproofing systems are often used to provide the requisite fire-resistivity to the primary and secondary framing systems.
Type III
Type IIIA and IIIB - Non-combustible exterior walls with a combustible (i.e., typically wood-framed) roof requiring either low or no fire resistant construction. Construction of this type is often either tilt-up warehouse type of construction with a wood subdiaphragm type roof. Type III construction has also become more common in mid-rise multifamily construction, using fire-retardant treated wood for exterior wall construction.
Type IV – Heavy Timber and Mass Timber
Type IV - Heavy timber construction with moderate levels of fire-resistant construction.
Type IV A/B/C - Mass timber construction, allowing mid-rise and high-rise construction from wood products. These types of construction will be found in the next edition of the building code, and earlier in some states.
Type V – Combustible
Type VA and VB - Constructed of any allowable material, including wood construction, with low or no fire-resistant construction. Type V-A requires one-hour fire resistant construction throughout. Both Type V-A and Type V-B construction is typically constructed of light-frame wood or metal stud and joist framing. In North America, these systems are typically platform framed but can be balloon framed as well.
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Building Elements within Types of Construction
Each type of construction has assigned to it various fire-resistance ratings for various building elements, such as structural frame, bearing and nonbearing walls, floor assemblies, etc. For each type of construction and its subtype, there are minimum requirements for the hourly fire-resistance rating for each element. Regarding subtypes, subtype B is generally non-rated construction (except for in Type I) and subtype B is generally at least one hour rated. It should be mentioned that the ratings Table 601 are minimum ratings, and when ratings of a greater value are required elsewhere in the code, those higher ratings will govern. In addition, as the type of construction increases, generally the cost of construction will increase as well.
Types of Construction: the relationship to building areas and automatic fire sprinkler systems
The Type of Construction directly affects the amount of allowable floor area that a building may have. Table 506.2 shows how the allowable floor area varies depending on the sprinkler system installed, the number of stories the building has and the type of construction assigned. This table can either be used to analyze if a design correctly:
- Specifies the proper automatic fire sprinkler system based on Chapter 9
- If the building is within the fire area limits based on the sprinkler system provided for, and
- If the correct type of Construction has been assumed for the building.
In addition, the building heights and stories tables must also be consulted to similarly verify if the building is within the allowable heights and number of stories.
If these items are left to verify later into the design, the cost to the budget can be disastrous if a full redesign of the building is required, because the incorrect Type of Construction was selected. Alternatively, using these tables in an iterative manner can be time consuming if the building is not clearly a particular type of construction (such as a single family home or a tall high rise building).
Types of Construction: Two tools to provide efficiency in design and analysis
UpCodes provides multiple tools for assessing proper types of construction. One tool is the Construction Type Guide, found in the Project Input page of the code calculators. This guide will allow you to quickly try a number of different options in regards to sprinkler types and occupancy groups and areas to see which types of construction would be candidates for the building in question. If a more detailed analysis is needed, the building composition of single or mixed occupancy, single or multi-story buildings can be provided in the project input, and the Guide will show the various types of construction that may be allowed for that particular building type. Another tool, the Code Calculators, can provide detailed information about the compliance of a design.
In the following example, a Group B Occupancy building of 77,000 square feet with 3 stories and that has a building height of 45 feet with an NFPA 13 sprinkler system can use any type of construction. However, if the sprinkler system were to be eliminated, construction types IIB, IIIB, VA or VB could not be used.
History of Types of Construction from the UBC to IBC
Ever since the early days of the Uniform Building Code, buildings have been classified as one of five general types of construction to account for the relative fire safety inherent in various types of construction methods. In the United States, buildings are generally constructed of one of a few types of materials: concrete, steel, masonry or wood. While each of these materials with the exception of wood are considered non-combustible, each material has methods of construction that lend themselves to being more or less fire-resistant. In the building code, the types of construction are labeled types 1 through 5, denoted by roman numerals I, II, III, IV and V. The origins of this is found in the 1927 Uniform Building Code, the first edition of the building code developed for use on the United States west coast. The original classifications were:
Types of Construction (1927 UBC)
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The types were ranked by overall fire resistivity of the basic materials. Even though heavy timber is itself a combustible material, while metal frame is not, the inherent fire-resistivity of a large timber beam or column is much higher than an unprotected steel beam or column. After the 1949 Uniform Building Code, the types of construction then started moving to become ordered by combustibility of the material, with new fire resistivity ratings shown by 1-hour or non-rated sub-categories.