Having been nicely schooled on reasons not to put vapor barrier on my walls with exterior foam in zone 6, SE MN, I now wonder about the proper way to insulate the ceiling. This is a heated shop with a vented roof and scissors trusses. I would like to use ribbed steel panels for the ceiling, and have been given rolls of R38 unfaced insulation that I would place on top of the steel panels.
I would like to make this airtight, however, and I see two options. First, I could caulk the overlapping panel seams and use great stuff around the perimeter of the ceiling. Or, if could use polyethylene sheeting applied to the bottom chord of the trusses before putting up the steel.
The polyethylene sheeting seems like the easier option, and the one I would like to go with unless I'm overlooking some major design flaw in this approach. Thoughts?