Dry walling basement wall.

Old 10-16-17, 07:52 AM
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Dry walling basement wall.

Hi All, hopefully i'm posting this in the correct area. I asked this several months ago but the opinions were sparse so I thought i'd try it again hoping that maybe there will be some new thoughts. Our home is 6 months old with a walk out basement. The back basement wall is not concrete but framed (2X4's) all the way down to the approx. 8 inch high foundation on footing. Under the siding is your typical 1/2 inch sheathing covering the entire outside of the wall with your typical insulation between the studs on the inside. The inside wall then has a plastic sheet I will call a vapor barrier over the entire inside wall. During our final walk through our builder told us that if we dry wall that we should TAKE DOWN the plastic so everything can "breathe". Seems like All i've been hearing for the past 20 years is that vapor barriers are a MUST in wall situations. So my question is this......when dry walling a basement wall that already has a sheet of plastic over the entire thing, should one take the plastic off, or leave it on ?? Any thoughts would be greatly appreciated......Thanks
Old 10-16-17, 08:00 AM
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Yes, building science and popular opinion have changed over the years, but the poly probably is not hurting anything in your case. Just be observant if there is any sign of mold behind the poly, if there is, you might want to remove it.
Old 10-16-17, 08:31 AM
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Not sure if you are referring to just the stud portion of the wall or the concrete areas as well?
Dealing with the stud portion since it is all above grade the assembly can dry to the outside. The debate surfaces when you place a plastic vapor barrier over a concrete wall, with or without insulation, and now the wall cannot dry in either direction. For the concrete that does not present a problem, it likes being damp. But if any organic material is trapped under the vapor barrier it can become a source for mold, and fiberglass insulation can contribute.

Are we talking about just a stud wall assembly or studs in front of the concrete?

In all cases air sealing is an important part of preventing moisture movement.

Old 10-16-17, 08:45 AM
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There is a huge difference between vapor barriers and vapor retarders.

Plastic is a barrier, nothing gets through and that is where problems can exist if water is trapped on either side.

A Retarder simply slows down the movement but does not block.

Personally I would never use any kind of plastic sheeting on an exterior wall above or below ground. Hoses that are sealed tight, need special HVAC equipment to keep moisture in check.
Old 10-16-17, 08:56 AM
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I have also heard of installing the plastic between the studs & the drywall. That lets the concrete breathe & still keeps the moisture away from the dry wall.
Old 10-16-17, 11:56 AM
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Thank You for the responses, we are talking about a stud wall with a wood (or likeness...LOL) sheathing on the outside of the studs, and then vinyl siding is attached to the sheathing. The stud wall is on about an 8 inch tall foundation which is on your standard footing. This appears to be the way they are building rear walls these days on walk out basements, around here at least. Not sure why, got to be some sort of cost reduction involved. Less crete obviously, but more labor intensive and not sure what offsets what with the materials after wood, siding, insulation...etc. are all considered.

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