The applicable requirement is found in 2021 IBC Section 504.3 and Table 504.3. The table regulates building height in feet above grade plane by occupancy, construction type, and sprinkler condition. For a Group I-4 occupancy equipped throughout with a Section 903.3.1.1 sprinkler system, the applicable row is the sprinklered “S” row.
Reading across that row to Type IV-B construction gives a maximum building height of 120 feet. Therefore, option B is correct. The 180-foot value applies to Type IV-A construction for the same occupancy and sprinkler condition. The 85-foot value, which is not offered, applies to Type IV-C and Type IV-HT. The 270-foot value generally appears for certain lower-hazard occupancies—such as Groups A, B, E, F, M, S and U—when constructed as sprinklered Type IV-A, but it is not permitted for Group I-4.
This distinction reflects the additional life-safety considerations associated with custodial-care occupancies. A special inspector should verify that the approved construction documents identify both the correct occupancy classification and construction type because either classification directly changes the permitted height.
References/Topics: 2021 IBC Section 504.3; Table 504.3, Group I-4, sprinklered Type IV-B construction; Section 903.3.1.1.
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