Spray Foam / Condensation Concerns
I am currently renovating my home in northern Wisconsin (Zone 7A). The house was constructed approximately 50 years ago using conventional 2×4 framing, batt insulation, fiber board (Celotex type sheeting), and hardboard siding.
Due to health issues, the previous owner left the home in poor repair for about 2 years, resulting in some interior water damage and roof issues. I replaced the roof last fall and will be tackling the entire exterior later this spring.
I will be removing all of the existing siding, fiber board sheathing, and batt insulation. My plan was to keep the interior vapor barrier and add approximately 3″ of closed cell polyurethane spray foam insulation (applied from the outside).
Several of the local contractors have also recommended the addition of 3/4″ – 1″ of rigid foam to the exterior studs before sheathing with 1/2″ OSB and 8″ cedar lap siding. While I like the idea of eliminating thermal bridging through the studs, my concern is that there will be an air gap between the two layers of foam insulation (both of which have limited permeability).
In this scenario, wouldn’t I be creating an ideal situation for condensation to form between the two layers? We obviously live in a very cold climate and winter temperatures regularly reach -20 to -30 F.
I know that foam insulation is a heavily debated topic and I was hoping for some insight from some insulating professionals to this particular configuration. The usual phrase …. “we do this all the time up here” …. really doesn’t help me sleep at night!