If the decision is made to utilize a vented attic with insulation installed between the trusses, is a membrane on the underside of the truss required or recommended? Below the trusses will be an acoustic ceiling grid. The IBC construction type is V-B, so a rated roof with a rated membrane is not required. If a membrane is not installed, what are the side-effects? What membranes could be used besides GWB? Tyvek?