AEC definitions
Construction type is the building code's classification of a building's resistance to fire, based on whether the structure is combustible and what fire ratings the frame, walls, and floors have. Types run from Type I, the most fire-resistive, to Type V, ordinary wood frame. Together with occupancy, it sets allowable height and area.
Definition
IBC Chapter 6 defines the types. Table 601 states the required ratings for building elements. A building is the lowest type its actual construction meets. Calling a building Type II while the roof is unrated wood does not make it Type II. The code sheet must match the wall sections and the structural notes. Sprinklers can increase allowable area. They do not, by themselves, change the construction type. Local amendments edit the tables. Use the adopted code.
In depth
If the columns are noncombustible and rated but the floor assembly is not, you do not get the type the columns would have allowed. The type is a package.
Protected and unprotected subtypes, such as II-A and II-B, differ by whether elements are rated. The letter is not decoration.
Wall sections, structural notes, and a rating schedule should make the Table 601 hours visible. A code sheet that says Type I-A while details show exposed wood structure will draw a comment.
Penetrations and joints have to preserve the rating. The type is lost at the unsealed hole.
The tables give a base. Frontage and sprinklers may increase it. Mezzanines and unlimited-area provisions are specific sections. Cite them on the code sheet.
A story added in design development can change the required type. Recheck before the structure is priced.
A renovation does not automatically upgrade Type V to Type I.
The existing building code says when an upgrade is required, often at a change of occupancy or a large alteration. Read that path before promising a light remodel.
Examples
The code sheet states Type II-B. Structural notes specify noncombustible framing. No hourly rating is claimed for the frame, matching the unprotected subtype.
A wood roof on an otherwise noncombustible building pulls the type down. The code sheet is corrected before permit.
Sprinklers increase allowable area. The construction type line on the code sheet stays Type V-A.
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