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Suggestions on insulating a cantileved bay? Our builder stuffed them w/ fg batts. I’m sure they provide some insulation, but do nothing to stop the wind. There is plywood on the bottom of the joists, and access to them from the basement.
so my real question is… how to stop the massive air infiltration.
My thought was expanding foam in a can. They have regular formula, and triple expanding. If I use this, can I skip 4 mil poly? Should I fill the bay w/ foam, or fill a bottom layer (and on rim joist), then fill w/ fg batts?
Thanks.
Replies
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Canilevers that are open to the basement should NOT have filled joist cavities. To insulate these cants, lay R-13 or 19 flat into the joist bays and up the outer rim joist. Leave the space above the insulation open to accept the warm air from the basement. If you are getting drafts through the cantilever, you have got a sealing problem. The walls, rim and underside of the cantilever should be sealed or housewrapped, depending on what is done with the rest of the house. The underside should have plywood covering the joists, sealed well. If you have vinyl siding all of the exterior plywood should be caulked, housewrapped, sided and soffitted. I would remove the insulation and look for daylight showing or air movement, caulk these areas from the inside with a quality sealant and reinstall insulation as stated above. If you have hardboard or cementboard siding, be sure that it is caulked well on the exterior as well.
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Suggestions on insulating a cantileved bay? Our builder stuffed them w/ fg batts. I'm sure they provide some insulation, but do nothing to stop the wind. There is plywood on the bottom of the joists, and access to them from the basement.
so my real question is... how to stop the massive air infiltration.
My thought was expanding foam in a can. They have regular formula, and triple expanding. If I use this, can I skip 4 mil poly? Should I fill the bay w/ foam, or fill a bottom layer (and on rim joist), then fill w/ fg batts?
Thanks.