A layer of 1″ XPS foam between fiberglass batts?
I live in MN and am working on a complete interior remodel. The exterior walls are 2″x6″ w/ R19 fiberglass batt insulation, some with Kraft back & some with poly on the interior side. I would like to try & at least double the R value, but due to other design constraints would like to keep the additional interior intrusion to a minimum (exterior insulation is not possible).
Therefore, I’m thinking of installing 1″ XPS foam on the interior wall followed by a 2″x4″ wall filled w/ R13 fiberglass batts without any additional vapor barrier. My thinking is that the foam breaks up any thermal bridging & drastically reduces air movement while contributing to the overall insulating value.
My question is will I have condensate issues? My initial thoughts are that since since the more impermeable layer is more in the middle of the thermal envelope, thus kept warmer than the dew point, that any moisture that does develop on either side of that vapor barrier will be able to dry seasonally through the permeable exterior and interior layers.
This approach in theory gives me a total R-value of 38 while only adding an additional 4 1/2″ to my interior space. Does is sound like a reasonable approach?
Thanks much to any who take the time to give me some thoughtful advice!
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