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Firestopping of Concealed Combustible Spaces

Question asked by davis on Dec 27, 2019
Latest reply on Dec 27, 2019 by milt.werner

Chapter states:

“…ceilings are attached to the bottom of composite wood joists either directly or on metal channels not exceeding 1 in. in depth, provided the adjacent joist channels are firestopped into volumes not exceeding 160 ft3 using materials equivalent to ½” gypsum board, and at least 3 ½” in of batt insulation is installed at the bottom of the joist channels when the ceiling is attached utilizing metal channels.”


The construction in question is wood I-joists with resilient channels and 5/8" Type C gyp per IBC 720 prescriptive assembly.


In previous construction in the jurisdiction in question, we have not had to seal small penetrations in I-joists to create 160 ft3 concealed areas (effectively fire-caulking every penetration in every 4th or 5th joist.  They are now requiring this in our latest hotel project.


Is it the intent of the code that the concealed spaces essentially be airtight and 100% isolated from adjacent concealed spaces?  


Interestingly, the Fire plan review official has told us that had we used the factory provided knock-outs in the I-joists for all penetrations, then they would not be requiring this.  This seems to indicate they believe there is some interpretation that allows at least some unsealed penetrations through adjacent concealed spaces.


Thanks in advance,