Foil Faced Exterior Insulation
We are remodeling a house that was built in 1983. The exterior of the home is all brick. The exterior walls are covered with 1″ of Foil Faced Insulation, there is no plywood sheathing on the house, only 1x wind bracing at various locations on exterior walls. Once the interior drywall was removed, I found R-13 Batt insulation in the exterior walls with a polythylene vapor barrier on all the exterior walls. The inside face of the insulation has quite a few small areas of visible mold caused from the vapor barrier. Most of the exterior walls will be stripped down to the studs, exposing the exterior Foil Faced foam. The foil face insulation is in good shaped and has a tongue and groove connection. With only 2×4 walls, what do you recommend going back in with for insulation? I am trying to decide between spray foam or Fiberglass Bibs with a Smart Vapor Barrier(Certainteed Membrain). We are in the middle of Climate Zone 5, about halfway between 4 and 6.
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Current code is R20 OR R13 + R5 (R 13 cavity plus R5 exterior insulation). I would install whatever your installer is good at using. If it's batts then insist on grade 1 level of install.
Do you even need a vapor retarder with foil faced insulation? The permanence of foil faced insulation is less than 1 .
I would suggest removing the foil faced foam and replacing it with Insultex housewrap. You will get the vapor barrier needed to prevent wood rot and also add a layer of insulation that is equivalent to an R-6. Also, add other types of insulation such as Rockwool in order to bring the R-value to 20. The Insultex is 1.5 mm thick and is easy to handle. The website is http://www.insultexhousewrap.com.
Foil faced foam is already a vapor barrier. Note that insultex is a problem product and NOT recommended. There are some other Q+As here linking to an article explaining where the FTC has sued insultex for false claims. I would not use their product.
I would not use spray foam in the wall. Spray foam isn't really worth using in a wall. I personally would use mineral wool, which is easy to work with, but you could use fiberglass batts (or fancier stuff like dense back cellulose). I would use a smart vapor retarder like Certainteed MemBrain on the interior, which will help to limit moisture getting into the wall while still allowing drying when needed.
Make sure you detail your drywall air tight, and make sure you seal any penetrations (wires, pipes) into those stud cavities. Between the air sealing and the smart vapor retarder you should have a much safer wall assembly.