When the footnotes are disregarded, the fire-resistance ratings assigned to the principal building elements of Type IV-A construction correspond to those of Type I-A construction . Option A is therefore correct.
IBC Table 601 assigns both Type I-A and Type IV-A a 3-hour rating for the primary structural frame , 3 hours for exterior and interior bearing walls, 2 hours for floor construction and associated secondary structural members , and 1½ hours for roof construction and associated secondary structural members . Interior nonbearing walls and partitions are generally rated zero by Table 601 unless another code provision requires a rating. Exterior nonbearing walls are governed separately based on fire separation distance.
The similarity in Table 601 ratings does not mean Type I-A and Type IV-A are otherwise equivalent construction types. Type I-A relies principally on noncombustible structural construction, whereas Type IV-A permits mass timber subject to the substantial noncombustible protection requirements of Section 602.4.1.
Types II-A, III-A, IV-C, and IV-HT have materially different Table 601 requirements, so options B, C, and D do not provide a complete rating match.
References/Topics: 2021 IBC Section 601 and Table 601; Types I-A and IV-A fire-resistance ratings.
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