Originally Posted by
Matthew Barnicle
Right, because otherwise there is hot air constantly infiltrating the space between floor and ceiling, right? Also, all insulation needs an air barrier, right?
Not an "air barrier", think of blown in (loose fill) insulation, it has no "air barrier", however, it should have a "vapor retarder" facing (the paper of foil on batts), otherwise, yes, the air will move through the insulation. Loose fill insulation is always placed "on" something, such as gypsum board, which serves as a vapor retarder itself, and certainly serves as a "air barrier" to some extent also, thus, gypsum board on the walls serves that same purpose. Not a "barrier", but a "retarder" in that is allows air and vapor to pass through it, albeit at a reduced rate.
So, yes, "something" (such as gypsum board) would need to be installed after the faced batt insulation was installed (not only to serve as a retarder, but to protect and cover the facing on the insulation, which is not allowed to be left exposed).
What about the exterior walls within the truss space between floors. I am assuming that needs insulation also, correct?
Correct. And, if not already insulated, that will be a job.