Using foam sheathing inside and outside a block wall
I am insulating (half way there) inside a concrete block barn I am renovating with 2″ EPS. This hides all the electrical conduit and boxes, I thought it very smart. I was planning to insulate the exterior with 1 1/2 ” rigid foam to get code R value, put strapping on that and then vertical wood siding. I see here on GPA where this will trap moisture that may collect between the foam and block.
Had I been just a little smarter ( I would have come here first for one thing), I would have tried to find a way to put all the insulation on the outside. I don’t have much roof overhang so I did not want to add 3.5″ plus sheathing and strapping.
Any ideas on how to proceed? I could use 2″ of rock wool, but concerned that would get saturated with moisture in a driving rain. Can/should I put house wrap over the rock wool?
The foam on the interior is glued. Should I cut my losses, remove this and insulate the exterior? I would be about 7-8″ from the drip edge of the roof. Gutters would be a nightmare with snow. I’m in the Catskills, NY
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Philip,
I can't recall any GBA articles that say that you can't put rigid foam on both sides of a concrete block wall. This approach isn't much different from an ICF wall. There are no moisture concerns -- as long as you know how to install flashing, and what a water-resistive barrier (WRB) is.
By the way, you can't bury any electrical junction boxes in a wall. If the electrical box has a cover, it has to be accessible.
To clarify Martin's electical comments: "can't bury electrical junction boxes" means it's against electrical code. The idea is that it can be difficult to troubleshoot any future problems if the boxes aren't accessible. But if they were originally surface mounted boxes, and they become recessed, with the cover flush with the new wall surface, so they are still visible and openable, that's fine. And "if it has a cover, it has to be accessible" is true, but if it doesn't have a cover, it needs one put on, and it still needs to be accessible.