The IBC Table 722.6.2(1) states that 1/2" gypsum has a fire resistance rating (FRR) of 15-minutes, while 3/8" OSB (the product used for TJI joist webs) is 5-minutes.
NFPA 13-2019 Section 18.104.22.168.5.2(4) Item (10) discusses an exception to hydraulically calculating the system at 3,000 sqft remote area if joist channels are firestopped into volumes not exceeding 160 cubic feet.
Most volumes created by composite wood joists are much smaller than the 160 cubic feed stated in the standard, which means that gypsum board would only be required every 4th- or 5th- joist in most situations.
However, would the 3 or 4 layers of 3/8" OSB (the web of each joist) across 3- or 4-bays meet the equivalent of the 1/2" gypsum requirement?
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