I have a gutted bathroom, and am in the process of insulating. The walls in question are exterior walls. I am intending to put 6mil poly over the insulation. I have a bunch of paper faced insulation from another project. I was under the impression I should not use the poly vapor barrier with the faced insulation.
Someone mentioned just cutting the facing of the insulation after installing it before putting the poly vapor barrier up. Is this an ok technique?
All the faced "insulation", and I use that term loosely if you are referring to fiberglass batts, I've seen is cut a tad narrow; the stapled facing holding it tight-ish to the studs. If you remove the face, it likely won't fit tight. The double vapor barrier won't hurt when they are tight together. THAT SAID, you probably don't want a vapor barrier anyway (the poly). They are not being advised in most places in the country any more. Search here, on buildingscience.com, etc. Myself, if your left-over "insulation" is FG batts, send it to the dumpster and get some better insulation. Cotton, wool, mineral wool, or cellulose batts, if you don't want to dense pack either cellulose or FG. Check w/ local codes folks, and if they say "You need poly" ask them to read the regs to you. It very possibly says "A vapor retarder of 1 perm or less." Google airtight drywall approach, air barriers, etc, and look on the bs site I mentioned.