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Old 02-13-2015, 04:35 PM   #1
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Replacing poly vapor barrier when you can't access the whole thing?


I have part of a basement wall (with a block halfwall behind it) that I'm repairing on the inside. I have about a 4x5' section of sheetrock to replace. Behind that, I replaced the below grade insulation with foam board insulation. For above grade, there is some fiberglass roll insulation that is a bit shredded and has mouse tunnels through it, so I was going to replace a few feet of new insulation.

I have a few questions. If I'm just replacing a few feet of the roll insulation, should I use Tuck tape or similar to tape the new insulation to the old roll insulation, to keep everything in place? I can't access the top of the wall, so can't replace the whole roll in each stud bay.

Also, I'm in Minnesota, and the existing poly vapor barrier is rather loose fitting (i.e., not secured around electrical outlet boxes or circuit breaker panel) with some holes in it and some tears at the bottom. However, I can't access the whole wall or the whole sheet of poly. Would it work well to just Tuck tape a section of a new poly barrier to the old sheet, and to fix any tears in the old sheet with the tape? Also, I assume I can just use the tape to adhere the barrier properly to the sides of the electrical box and the breaker panel, and anywhere else it is loose where it can't be stapled, correct?

Any tips on replacing the insulation and part of the vapor barrier would be appreciated!
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Old 02-14-2015, 08:28 AM   #2
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Are there any moisture issues? Normally, poly in a wall is a recipe for condensation and mold/mildew.

No need to tape the insulation together. Just form fit it and overlap the seams so that you have full coverage.

If the plastic is largely intact and you don't have moisture issues behind it, just tape the patch to it.

Keep in mind, that type of wall design (depending on what you have on the exterior for cladding) is typically frowned upon now.

Be sure to not create a vapor trap with the foam board and plastic as well. If the wall can dry in either direction, that is a recipe for a problem.
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Old 02-14-2015, 10:32 AM   #3
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No moisture issues now ... we previously had some rain water seeping in on the floor during heavy rains, which is why I'm redoing the wall. But we re-sloped the ground around the outside to fix that.

Yes, I don't plan to put poly over the foam board, since the foam is already its own vapor barrier.

The reason we have a half block wall in the basement is because it's a split level, walkout home. Thanks for the tips!
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Old 02-14-2015, 12:03 PM   #4
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Good luck with it and stay warm up there.
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