e faced batts for the second layer. If you do, you run the risk of creating a double vapor barrier; any moisture that passes through the first layer of insulation can get trapped by the vapor barrier on the second layer.
For the most part, attics are insulated with blown-in insulation. So you might be wondering where the vapor barrier is. Actually, there isn’t one in that case, other than the drywall and paint on the ceiling. The difference between the attic and the exterior walls is that the attic isn’t a closed cavity. It’s open to the outside, and has ventilation to allow the moisture to escape. That’s why it’s critical that attics be properly ventilated, and that exhaust fans not be vented into attic spaces.
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-mil 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 [email protected]. All product reviews are based on the author’s actual testing of free review samples provided by the manufacturers.
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