Cold climate location (northern MN) I finally have a house with foil faced insulation added over what is probably OSB sheathing, behind newly installed vinyl siding. They did not use fan-fold insulation. I’m not sure of the foam insulation thickness, maybe 1/2 inch.
I know this is not an issue with 1/2 inch blue foam, but this is foil faced foam.
My thinking is this creates a double vapor barrier. There appears to be a poly air/vapor barrier on the heated side of the wall, plus drywall. The wall insulation is 5 1/2 inch fiberglass batts.
I’ve talked to several knowledgeable builders over the years, and the thinking is that this is a double vapor barrier. I’m thinking this is a serious concern; trapped moisture within the insulation cavity will eventually form mold. There is no direction, in or out, for moisture to dry from the wall cavity.
Any opinions from northern builders, especially Canadian builders?? What documentation is available to put this issue at a high level of concern? This is at the edge of my building science knowledge, and I’d like some knowledgeable opinions.