Replace vapor barrier?
I’m replacing some drywall in the corner of my basement – just one sheet on each wall. The block wall on one side (Northeast) is all below grade. The wall on the other side (Northwest) is half below grade. The bottom plate/block connection is not well sealed, so I was going to do that. The builder had a put a piece of poly up over the studs and fiberglass batts on the above-grade portion. the outer sheathing is right behind them. Should I replace this piece of poly or should I leave the fiberglass and studs exposed to increase drying to the inside? I wasn’t sure if the warm air in the basement would move more easily through and condense on the sheathing.
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Where are you? In general, poly is being avoided any more, except in very cold places (and often there, too). If it is only one sheet, then it is probably a coin toss. Be sure to air seal, though; that is what is critical. No, do not leave the studs exposed; air seal. Were I you, I'd read about this on buildingscience.com, and/or search here. Good luck, too.
Michael,
As John pointed out, you usually don't want any interior poly, but you do want careful air sealing. Knowing your location or climate would be useful.
You mention that your builder insulated the above-grade portion of the wall. Did the builder also insulate the below-grade portion of the wall? If so, what type of insulation was used?
In general, fiberglass batts should never be used to insulate a basement wall. However, in your case, correcting this error -- assuming there is some below-grade fiberglass -- would be difficult and expensive.
I am in Omaha, NE. The below-grade portion of the wall is not insulated. The furring strips are nailed directly to the block wall. If I remove the strips, add rigid foam, and then nail the strips back on, I'd have to replace the entire wall to adjust for the thickness.
Michael,
If all you are doing is replacing a few sheets of drywall, it hardly matters what you do.
If you want to address the thermal deficiencies of your walls, however, the following steps would be helpful:
1. Perform air-sealing work on all walls -- this is the minimum level of work.
2. If you can afford to, strip all of the drywall; insulate the below-grade portion of the wall with an adequate thickness of rigid foam insulation; and insulate the above-grade portion of the wall with the insulation material of your choice -- preferably not fiberglass batts. Then cover the walls with new paperless drywall, paying attention to airtightness.
Martin,
You say that fiberglass batts are to be avoided in a basement - would you add why or post a link? I thought Building Science's web site showed fiberglass over a layer of EPS as acceptable.
Thanks,
Erich
Erich,
I don't always agree with the BSC.
Fiberglass batts over rigid foam (in a basement wall) are certainly better than fiberglass batts touching concrete. Even better is rigid foam without any fiberglass batts.