I have a seldom used 1/2 bath. While trying to remove 3 layers of very ugly wallpaper, I discovered mold in the insulation in the outside wall. That wall has been stripped down to the studs, and we are putting it back together. The wall is currently insulated (R15 fiberglass on a paper backing.)
I was looking up the current recommendation for a vapor barrier inside of that. The little bit of construction I’ve ever done included stabling an impermeable plastic sheet inside of the insulation, below the sheet rock. So not totally sealed. Some of what I was reading now said that unless I can come close to fully sealing a vapor barrier, all the way around, that current practice says that this practice might be better skipped, as it could trap moisture inside the wall, exactly what I don’t want, and lead to mold.
The house is almost 50 years old. The outer siding is cedar siding that was painted at some point. There is not any kind of house wrap between the siding and the studs.
The room is a 1/2 bath, 4 1/2’ x 6 1/2’, containing a recently replaced casement window. There isn’t a shower or tub, and it gets used a few times a week.
The 1/2 bath has no outside venting, except the window.
I live in a Minnesota, a cold climate with winters that have several months below freezing.
Am I better off using a vapor barrier or not? If yes, do I need to do something like double side tape all the edges, in addition to stapling?