The International Building Code sorts buildings into five construction types, I through V, by how combustible the structure is and how long it must resist fire. Types I and II are noncombustible, Type III has noncombustible exterior walls, Type IV is heavy or mass timber, and Type V allows any material. Subtype A carries higher ratings than B.
Last reviewed October 2026
Helonic is an AI construction drawing analysis platform for teams researching construction types guide during drawing review. Below: the IBC 2021 Table 601 ratings for every type, what sets each type apart, and how sprinklers and frontage change allowable height and area.
IBC 2021 Table 601 sets the hourly rating for each building element, from 3 hours for a Type I-A frame down to 0 for Type II-B, III-B, and V-B. Values are in hours.
| Type | Combustibility | Primary structural frame | Exterior bearing walls | Interior bearing walls | Floor | Roof | Typical use |
|---|---|---|---|---|---|---|---|
| Type I-A | Noncombustible | 3 | 3 | 3 | 2 | 1½ | High-rise buildings, hospitals |
| Type I-B | Noncombustible | 2 | 2 | 2 | 2 | 1 | Mid-rise offices, schools |
| Type II-A | Noncombustible | 1 | 1 | 1 | 1 | 1 | Low-rise commercial |
| Type II-B | Noncombustible | 0 | 0 | 0 | 0 | 0 | Warehouses, big-box retail |
| Type III-A | Noncombustible exterior walls, interior any permitted material | 1 | 2 | 1 | 1 | 1 | Wood-frame apartments with rated exterior walls |
| Type III-B | Noncombustible exterior walls, interior any permitted material | 0 | 2 | 0 | 0 | 0 | Small commercial with masonry walls |
| Type IV-A | Mass timber with noncombustible protection | 3 | 3 | 3 | 2 | 1½ | Tall mass timber |
| Type IV-B | Mass timber, limited exposed timber | 2 | 2 | 2 | 2 | 1 | Mid-rise mass timber |
| Type IV-C | Mass timber, exposed timber permitted | 2 | 2 | 2 | 2 | 1 | Low and mid-rise mass timber |
| Type IV-HT | Noncombustible exterior walls, heavy timber interior | HT | 2 | 1 or HT | HT | HT | Heavy timber, mill buildings |
| Type V-A | Combustible (any permitted material) | 1 | 1 | 1 | 1 | 1 | Protected wood-frame apartments |
| Type V-B | Combustible (any permitted material) | 0 | 0 | 0 | 0 | 0 | Unprotected wood frame, small commercial |
Source: IBC 2021 Table 601. HT = heavy timber sized per IBC 2304.11. Table 601 footnotes change several values, for example letting the frame and bearing walls drop by 1 hour where they support only a roof, so read them before applying a number. Exterior nonbearing wall ratings come from Table 705.5 and depend on fire separation distance. Check the edition your jurisdiction adopted.
Type of construction classifies a building by the combustibility and fire resistance of its structural elements. It works together with the IBC occupancy classification: occupancy group plus construction type sets how tall and how large the building can be.
IBC construction types I through V are distinguished by whether the structure is noncombustible and how much fire resistance those elements must have.
Steel or concrete structure with the highest ratings in Table 601. Type I-A has no height limit, and Type I-B covers most mid-rise and many high-rise buildings.
Steel or concrete structure with low or no ratings. Type II-A carries 1-hour protection; Type II-B is unprotected. Common for warehouses, retail, and low-rise offices.
Exterior walls are noncombustible, typically masonry or concrete, and the interior structure can be wood. IBC 602.3 also allows fire-retardant-treated wood framing in exterior walls rated 2 hours or less.
Type IV-HT is traditional heavy timber, where large member sizes give the fire resistance. The 2021 IBC added Types IV-A, IV-B, and IV-C for mass timber such as CLT and glulam. For most sprinklered occupancies, Table 504.3 allows 270 feet for IV-A, 180 feet for IV-B, and 85 feet for IV-C.
Any material the code permits, including light wood framing. Type V-A requires 1-hour protection of the structure; Type V-B has no rating requirements.
Height and area limits can increase with sprinklers, frontage, and some mixed-occupancy calculations allowed by the IBC.
An NFPA 13 system typically adds one story and 20 feet of height, and Table 506.2 sprinklered area factors run three to four times the nonsprinklered value.
Open perimeter access for firefighting can increase area up to 75% (IBC 506.3)
Certain combinations of sprinklers, frontage, and low-hazard uses allow unlimited area (IBC 507)
Both are noncombustible, but Type I-A carries higher ratings in IBC 2021 Table 601: 3 hours for the primary structural frame and bearing walls against 2 hours for Type I-B. Type I-A has no height limit, while Type I-B is limited to 180 feet for most occupancies when sprinklered.
Yes. Type III requires noncombustible exterior walls, and interior structural elements can be any material the code allows, including wood framing. IBC 602.3 also allows fire-retardant-treated wood framing in exterior walls rated 2 hours or less, which is why many wood-frame apartment buildings are Type III-A.
They are the mass timber construction types added in the 2021 IBC. All three use mass timber such as cross-laminated timber for the structure. Type IV-A requires noncombustible protection over the mass timber, Type IV-B allows limited exposed timber, and Type IV-C allows exposed timber except in shafts and concealed spaces.
An NFPA 13 system typically adds one story and 20 feet of height under IBC Tables 504.3 and 504.4, and the sprinklered area factors in Table 506.2 run three to four times the nonsprinklered value. For example, a Type V-A building limited to 50 feet without sprinklers can reach 70 feet for most occupancies when fully sprinklered.
Note: Local jurisdictions may have amendments to the IBC. Always verify requirements with your Authority Having Jurisdiction (AHJ).
Related references for code compliance, occupancy, and fire-rated assemblies.