I'm working on re-insulating the exterior walls of my second-floor bedroom since they're really cold during the winter. The current insulation is old, brittle fiberglass batts from the 60s behind drywall. I'm leaning towards using rockwool for the new insulation, but I'm confused about the vapor barrier. I live in Northern Illinois where winters are harsh. Should I go with 6mm plastic for the vapor barrier, or is there a better option, or should I skip it altogether?
1 Answer
Typically, the vapor barrier should go on the warm side of the wall, which in your case would be the inside. I suggest reinstalling what was there previously. If there wasn't a barrier before and there are no issues with moisture in the walls, you might not need one. If the old insulation was paper-faced, that acted as a vapor barrier, so if you switch to rockwool, then using 6mm plastic would be a good choice. Just keep an eye out for any hidden framing or moisture issues when you open up the walls.
Got it! So since the insulating was paper-faced before, I should definitely add the plastic with the rockwool.