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I’m renovating an old house, and came upon a problem (surprise, surprise!). The rafters are 2×4 on knee walls, and anywhere from 16″ O.C. to 20″ O.C.
If we use 15″ insulation batts, with kraft vapor barrier, there is still a space next to these to fill in. I know I can use 24″ wide batts, but lets say I don’t have them on hand. If I use the 15″ bats with kraft vapor barrier, and then “stuff” the 1~2″ gaps next to these with unfaced insulation, what may happen, with regards to moisture? Or, what would be the concern if I were to cover this kraft vapor barrier completely with plastic sheet vapor barrier? I also read a discussion that included strapping the rafters and installing 1-1/2″ rigid foam across the 2×4 rafters, to add an additional amount of R-value. Can I install the rigid foam over the kraft vapor barrier? Would this foam then act as the vapor barrier? I am concerned with causing moisture problems, under the guise of “improvement”. Thanks!
Replies
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I'm renovating an old house, and came upon a problem (surprise, surprise!). The rafters are 2x4 on knee walls, and anywhere from 16" O.C. to 20" O.C.
If we use 15" insulation batts, with kraft vapor barrier, there is still a space next to these to fill in. I know I can use 24" wide batts, but lets say I don't have them on hand. If I use the 15" bats with kraft vapor barrier, and then "stuff" the 1~2" gaps next to these with unfaced insulation, what may happen, with regards to moisture? Or, what would be the concern if I were to cover this kraft vapor barrier completely with plastic sheet vapor barrier? I also read a discussion that included strapping the rafters and installing 1-1/2" rigid foam across the 2x4 rafters, to add an additional amount of R-value. Can I install the rigid foam over the kraft vapor barrier? Would this foam then act as the vapor barrier? I am concerned with causing moisture problems, under the guise of "improvement". Thanks!