Rigid foam over kneewall studs to eliminate thermal bridging?
Hello! I've got a 1926 bungalow in Portland, OR (zone 4C). The attic was finished in the 50's, and is terribly leaky and not insulated. The previous owners left behind a boatload of fiberglass batts, unwrapped, with kraft paper backing. I was hoping to use them to insulate the kneewall, after air-sealing the gaps with some caulk.
However, since the joist bays are somewhat shallow (I believe ~3.5"), I was hoping to cover the outside of the studs with rigid foam insulation as well (XPS or ISO) to prevent thermal bridging, secured in place with a polyurethane expanding foam.
My concern is that this scenario would have a vapor retarder against the warm space (in the form of the kraft paper) and a vapor retarder/barrier in the form of the rigid foam. Do you think that this could lend itself to trapping moisture in the wall? We don't have an upstairs bathroom, but Portland weather is all over the map, and we do have a fair bit of humidity.
Posted Wed, 09/25/2013 - 20:22
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