Insulating new construction cathedral ceiling and have already installed fiberglass batts R-38 (which is all I had room for) with air baffle in the ceiling. Seems as thou everybody you talk to has a different opinion on how to insulate cathedral ceilings. I'm not going into all the details and the why, but that part is done. But had the contractor stop by, to look at the job to install Nu Wool insulation in the walls. In conversation I mentioned that we were putting tongue and groove cedar on the walls and ceiling. He asked if we were putting dry wall underneath, I said no. His recommendation was to put dry wall or 1" of styrofoam underneath and tape the joints. His point was that the tongue and groove cedar would allow air to move through the walls and ceiling thus we wouldn't be happy with the fiberglass as an insulation. And have high heat loss. If this is true could I just put up plastic and accomplish the same thing which would limit air movement through the cedar?