Incorrect installation can trap moisture
The last area to consider is your crawl space, which actually has two vapor barriers to be concerned with. In the typical crawl space with a dirt floor, a 6-millimeter plastic vapor barrier is used to prevent moisture from the soil from coming up into the crawl space area. That vapor barrier is laid directly on the dirt, and the seams are overlapped at least 12 inches.
The other vapor barrier is created with your floor insulation. One common mistake people make when insulating a floor is to install faced batts between the floor joists with the Kraft paper facing down, so they can staple the paper to the joists to hold the batts in place. Remember, the paper is the vapor barrier, and it has to face the heated part of the house, which means it has to face up. Always install batt insulation between the joists with the paper facing up against the underside of the subfloor, then hold the insulation in place with lath, wire or other means.
Remodeling and repair questions? Email Paul at firstname.lastname@example.org. All product reviews are based on the author's actual testing of free review samples provided by the manufacturers.
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