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lerichmond 09-29-2012 09:20 AM

basement insulation
Can I use batts of fiberglass insulation directly against a basement wall with paper barrier on the outside? There does not seem to be a moisture problem, but I painted the concrete walls with dry-lock to be sure there is no leakage.

AllanJ 09-29-2012 10:23 AM

When there is a vapor barrier on the wall, either Dry Lok on the inside surface or black goop on the outside surface, there should not be another vapor barrier.

Therefore, if you use faced (vapor barrier) fiber glass insulation, cut out slots or squares of the paper here and there leaving the fiberglass batting exposed. At least 25% of the total paper area should be removed although enough paper should be left so the batt does not sag or fall down.

Experts argue long and loud over leaving an air gap of at least an inch between the fiber glass batt and the concrete wall. While moisture seeping in from the outside may be prevented, moisture from the room air will find its way through the wall and condense on the concrete surface and it is better if the fiber glass does not touch the wall surface which may be wet from time to time.

A "second" moisture barrier on the inside surface will not cause a problem if the wall cavity space with the fiber glass batts is hermetically (perfectly) sealed which is almost impossible to achieve and maintain, hence everyone says that two vapor barriers is a no-no.

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