Most pre-engineered metal buildings are classified as Type II-B construction under the International Building Code: the steel frame is noncombustible, and the code requires no fire-resistance rating for it. That classification is common, not automatic. The same steel building can be Type II-A when its frame is fire-protected, or Type V-B when the design professional declares it that way, and the building official approves whichever type goes on the drawings.
Construction type sets how large a building can be and what has to be fire-rated, so for a pre-engineered metal building it is worth settling early, alongside the building’s use and size.
The five construction types at a glance
The IBC places every building in one of five construction types, numbered I to V, by the materials of its building elements and the fire resistance required of them. Chapter 6 of the 2024 International Building Code defines the types. Most come in an A version and a less fire-resistant B version.
| Type | Building elements | Frame rating (hours, Table 601) | Metal buildings |
|---|---|---|---|
| I-A, I-B | Noncombustible | 3, 2 | Rare |
| II-A, II-B | Noncombustible | 1, 0 | II-B usual; II-A if the frame is protected |
| III-A, III-B | Noncombustible exterior walls | 1, 0 | Uncommon |
| IV-A, IV-B, IV-C, IV-HT | Mass or heavy timber | 3, 2, 2, HT | No |
| V-A, V-B | Any permitted material | 1, 0 | V-B if declared, or with wood framing inside |
Why most metal buildings are Type II-B
A metal building is usually Type II because Section 602.2 of the IBC defines Types I and II as construction with noncombustible building elements, and the frames, secondary framing and panels of a PEMB meet that test. The code classifies a building by its materials and ratings, not by how the frame was engineered, so a PEMB and a conventional structural steel frame are classified the same way.
Metal buildings usually fall in the B version of Type II because nothing requires the steel to be fire-protected. Table 601 sets a zero-hour rating for the primary frame and the roof construction in Type II-B. Writing in The Construction Specifier, engineer Vincent Sagan, PE, notes that single-story metal buildings can generally be classified as Type II-B construction, which does not require fire protection.
Type II-B does not mean fireproof. Unprotected steel loses strength in a serious fire, so the code limits a Type II-B building more tightly than a Type II-A building. Use and location can also bring rated elements into an unrated building: a metal building less than 30 feet from a neighboring structure will typically need a fire-rated exterior wall, and a building that mixes uses, such as a brewery with retail, meeting rooms and a restaurant, may need rated walls between them.
Metal buildings can meet a fire rating when one is required. Testing for the Metal Building Manufacturers Association showed one- and two-hour ratings are achievable, mostly with gypsum board protection. A protected frame is how a metal building reaches Type II-A. Type I, with a two- or three-hour frame, is the classification for high-rises and very large buildings, and a single-story metal building rarely needs it.
When a steel building ends up Type V-B
A steel building can be classified as Type V-B even though its frame is noncombustible. Section 602.5 of the IBC defines Type V as construction of any materials the code permits, which includes steel. Section 602.1.1 adds that a building need not conform to a higher type than its occupancy requires, even when some of its features meet a higher type.
A steel building becomes Type V-B in one of two ways:
- By declaration. When a building fits within the Type V-B limits for its use, the design professional can declare it Type V-B. That can make sense when the building does not need the larger allowances of Type II-B, since Type V-B lifts the Type II limits on combustible materials such as wood framing.
- By accident. In Type I and II buildings, the IBC permits combustible materials only in listed uses. Fire-retardant-treated wood is allowed in nonbearing partitions, but ordinary wood stud walls are not. Offices framed in untreated wood studs can push the whole building to Type V-B.
The accidental route is the one to watch. A building takes a single construction type, and Type V-B allows roughly half the floor area of Type II-B for a typical warehouse. The building may work on opening day, but the first extension then has to fit the smaller Type V-B limits or be designed as a separate building. Office and mezzanine framing is worth deciding with the design professional before the interior is drawn.
Construction type isn’t the only classification
Construction type is only one of the classifications a building receives under the IBC. Risk category is the other, and for the manufacturer it comes first. Stephen Tanco, Universal Steel’s owner, says the main question on a new building is “What is the use?”:
“The use and occupancy of the building are used to determine the risk category in accordance with the applicable building code.”
Stephen Tanco, owner, Universal Steel
Section 1604.5 of the IBC sets four risk categories, which Stephen summarizes as I, low hazard; II, normal or standard; III, high occupancy; and IV, essential. Most buildings are Category II. Agricultural and minor storage buildings can be Category I, large public assembly buildings Category III, and fire stations, police stations and designated emergency shelters Category IV.
Risk category matters to a metal building because it feeds the design loads. Under ASCE 7, the wind, snow and seismic loads a structure is designed for depend on its risk category, and a higher category generally means higher loads. In Universal Steel’s design and engineering process, the building’s use, dimensions, location and loads are confirmed with the customer before the confirmation letter is signed.
The construction type, by contrast, is decided on the project side. The architect or engineer of record determines the construction type in the code analysis for the permit, and the local building official approves it. Universal Steel engineers the steel frame to the code and loads for the building’s use and issues the PE-stamped drawings, but the manufacturer does not set the construction type.
What the construction type changes for the owner
Construction type sets a building’s size limits, together with its occupancy and whether it is sprinklered. For a typical warehouse, classified as Group S-1 (moderate-hazard storage), the 2024 IBC sets these limits:
| Group S-1 warehouse | Type II-B | Type V-B |
|---|---|---|
| Stories, not sprinklered | 2 | 1 |
| Stories, sprinklered | 4 | 2 |
| Height, not sprinklered | 55 ft | 40 ft |
| Height, sprinklered | 75 ft | 60 ft |
| Area factor, not sprinklered | 17,500 sq ft | 9,000 sq ft |
| Area factor, one story, sprinklered | 70,000 sq ft | 36,000 sq ft |
The area factors come from Table 506.2 of the IBC, before any increase for open frontage. For the same warehouse, Type II-B allows roughly twice the floor area of Type V-B, and sprinklers roughly quadruple what either type allows on a single story. States and cities adopt and amend different editions of the IBC, so the design professional works from the code in force locally.
Under Section 507.4 of the IBC, a one-story building in Group B, F, M or S (business, factory, mercantile or storage), of any construction type, has no area limit when it is sprinklered throughout and surrounded by public ways or open yards at least 60 feet wide. For large metal warehouse buildings, factories and stores, the sprinklers and the site layout can matter as much as the construction type.
Frequently asked questions
What is Type II-B construction?
Type II-B construction is a building whose building elements are noncombustible, such as steel, with no fire-resistance rating required by Table 601 of the IBC. Type II-B is the usual classification for a single-story metal building with an unprotected steel frame.
What is the difference between Type A and Type B construction?
The A version of an IBC construction type requires more fire resistance than the B version. Type II-A needs a one-hour primary frame and Type II-B needs none. Types III and V follow the same pattern, while Type I-B still requires a two-hour frame.
What insurance construction class is a metal building?
Insurers use their own construction classes, separate from the IBC. Under the six ISO categories, summarized in IRMI’s definition, a building whose exterior walls, floor and supports are metal or other noncombustible materials is Noncombustible, Construction Code 3. The insurance class does not change the IBC construction type on the drawings.
Settling the construction type early
The construction type of a metal building follows from early decisions: use, size now and later, sprinklers, distance to neighbors, and how the inside will be framed. Settled with the design professional before the frame is engineered, those decisions give a construction type that fits the building and leaves room to grow. See how Universal Steel engineers and manufactures its pre-engineered metal buildings to the code and loads of each project.
