ice and frost on vapour barrier


Old 02-25-03, 09:35 AM
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Question ice and frost on vapour barrier

I am in the midst of finishing my cold weather basement.

The house was built in 1998 and the builder insulated the exterior basement walls by applying an exterior vapour barrier against the concrete foundation and then built 2X4 walls around the exterior using fibergalss batts and the an additional interior vapour barrier.

As I lifted the inner vapour barrier i realized that in some areas there was frost and even some ice on the inside facing side of the exterior vapour barrier. I have found that the walls are built approx 2" away from the concrete walls and there is a gap between the top of the walls and foundation where air can get behind the insulation and down the back side of the inner insulated wall.

I assume this is the root of my problem and i should seal that opening which is allowing the warm house air to get in contact with the cold exterior wall.

Can anyone confirm or provide suggestions?

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Old 02-25-03, 10:27 AM
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There should be only one vapor barrier. Otherwise, moisture will be trapped between them and condense. Then it may freeze or give rise to mildew and mold.

Ordinarily, the vapor barrier is on the living space side of the insulation. This is not true everywhere.

If you have an exterior concrete wall, then vapor barrier, then insulation, then vapor barrier, eliminating the vapor barrier on the exterior wall seems to be the best approach.

Since the plastic enclosed batts of fiberglass insulation sold by Owens-Corning have slits cut in the plastic and are described as not being vapor barrier, then it seems reasonable that slitting the vapor barrier on the exterior concrete wall would serve to eliminate it.

I am no expert on this topic. You may be best served by waiting for someone with more knowledge in vapor barrier modification to come along and assess the issue of how to come up with only one vapor barrier in your case.

Hope this helps.
Old 02-25-03, 10:30 AM
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By-pass Phenomena

You are correct, heat is getting pass the insulated wall. Seal the top of the wall to prohibit the heat from getting around it.
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