If that is a fire rated wall assembly, that OSB is not going to cut it.

Both sides of that fire rated wall need to be 5/8" Type X gypsum board.

Also, that opening into the attic should be firestopped.

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Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com