IBC Construction Types: Type I-V Explained for Permits

Section 602 requires every building to be classified into one of the five types defined in Sections 602.2 through 602.5. Here is the plain-language version, based on the 2018 and 2021 editions of the code text.

Two details matter here. The difference between Type I and Type II is not the material. Both require noncombustible elements. The difference is the fire-resistance ratings in Table 601. And "noncombustible" applies to the elements Table 601 lists, so a Type II building can still have some combustible items where Section 603 allows them.

The order also tracks fire performance. Type I is the most stringent and Type V has the fewest material requirements.

In the 2018 IBC, Types I, II, III and V are each split into an A and a B subtype. That gives you IA, IB, IIA, IIB, IIIA, IIIB, VA and VB. Type IV is shown as IV-HT in that edition.

The letter tells you the degree of fire resistance required for building elements and assemblies. A is the more protected version and B is the less protected one. A Type IIB building and a Type IIA building use the same family of noncombustible materials, but the IIA building needs more hours of rating on its structural frame, floors and roof.

Use this rule of thumb when you read a drawing set:

1. The Roman numeral tells you the material family.
2. The letter tells you how much protection that family gets.
3. Table 601 gives you the actual hours, element by element.

Read the hours from the code edition your jurisdiction has adopted. The ratings and footnotes in Table 601 have changed between editions, and some cities publish their own amended version. We don't list hour values in this guide for that reason. Copying a number from a different edition is a common way to get a plan check comment.

In the 2012 through 2018 editions, Type IV is heavy timber. Exterior walls are noncombustible, and interior elements are solid or laminated wood, heavy timber or structural composite lumber without concealed spaces.

The 2021 edition restructured the type. Section 602.4 now covers mass timber, with subtypes IV-A, IV-B, IV-C and IV-HT, and fire-resistance ratings that come from Table 601. Exterior walls can also use other materials permitted under 602.4.1 or 602.4.2, such as fire-retardant-treated wood or cross-laminated timber.

If your project involves mass timber, confirm which edition your jurisdiction enforces before you pick a subtype. A jurisdiction still on the 2018 IBC will not recognize IV-A, IV-B or IV-C. Check the 2021 Chapter 6 text from ICC against the 2018 text to see the difference side by side.

The construction type limits allowable height, floor area and combustible materials. It also interacts with your occupancy classification, sprinkler status and fire separation distance. Reviewers read these together, so a mismatch anywhere shows up as a comment.

Here is how the type usually surfaces in review:

• The cover sheet or code summary. The reviewer checks that the declared type matches the framing shown in your structural sheets. A Type IIB declaration with wood roof framing on the plans is a flag.
• Fire-resistance rating notes. Rated walls, floors and the structural frame are checked against Table 601 for the declared type.
• Area and height. The type is a column input to the height and area provisions, so an upgrade from VB to VA or from V to III can be how a design gets more floor area.
• Material callouts. Combustible items in a noncombustible type must fit one of the exceptions in Section 603.

Section 602.1.1 also helps you. A building doesn't have to meet the details of a higher construction type than its occupancy requires, even if some of its features exceed that type. If you are designing to Type IIA but only need IIB, your reviewer can classify the building by the lower requirement.

For a worked view of what reviewers flag before you submit, see what plan check correction tracking covers. If a comment on construction type does land in your correction letter, respond to it with a matrix that points to the code section and the sheet you changed.

Follow these steps before you stamp the cover sheet.

1. Find the adopted code edition. Your building department's website lists the IBC edition and local amendments in force.
2. Identify the occupancy classification. The type has to satisfy the height and area limits for that occupancy.
3. Pick the structural system. Concrete or steel frame points to Type I or II. Masonry exterior walls with wood interior framing points to Type III. Wood frame throughout points to Type V. Timber with large solid or laminated members points to Type IV.
4. Read Section 602 for your edition. Match your system to the definition, not to a nickname.
5. Read Table 601. Write down the rated hours for each element of your chosen subtype from the table in your adopted edition.
6. Check local amendments. Some cities modify the subtypes or add their own. Search your jurisdiction's amendments for "Chapter 6" or "Table 601".
7. State the type on the cover sheet. Include the section number and edition so the reviewer can follow your logic.

Treating "noncombustible" as one tier. Type I and Type II are both noncombustible. Choosing between them is about fire-resistance hours.

Using a table from the wrong edition. Table 601 values and footnotes differ across editions. Pull it from the code your department enforces.

Assuming Type IV means any timber building. Under 2018 rules, Type IV is a specific heavy-timber definition with no concealed spaces. Under 2021 rules, it is the mass timber family with its own subtypes.

Forgetting local adoption. Many states and cities adopt the IBC with amendments. The model-code section numbers here are a baseline. Your jurisdiction's amendments may differ; for a local example, see the Los Angeles building permits page.