Add exterior foam — but paper-faced batts?
I am about to replace the windows on one side of my house, which for various reasons will require removing my existing siding. I also have in my possession a whole bunch of 3 inch foil faced polyiso foam board, the perfect opportunity to add an R19 layer of foam on top of my existing 2 x 6 walls with fiberglass batts. Problem is, I’m sure the batts have kraft facers on the interior. So I’d be creating a vapor barrior sandwich.
So what are my options? Here are 5 that come to mind,
1 – I could of course do nothing, which dramatically simplifies things.
2 – I could remove the sheathing, cut out the kraft paper, put the batts back in, and then add the foamboard, but boy that’s a ton of work.
3- If I only needed an inch or maybe 1.5 of XPS or EPS, that might be just permeable enough, but in my zone 5/6 area with 2×6 walls I would need 2.5 inches of XPS to avoid condensation, which is then basically impermeable.
4 – Just put up the foam, make sure its flashed well with a WRB, and hope I don’t get any water infiltration.
5 – What if I drilled a number of 1/8 inch holes from the interior, through the drywall (and kraft paper) in each stud bay? Easy to patch, and I’ll be painting anyways. That should add some permeability just in case water ever gets in there. Of course, more vapor will get in there, but with R19 foam on the exterior I should have no condensation.
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