Risk of Moisture with Interior Rigid Foam
user-7692346| Posted inEnergy Efficiency and Durabilityon
I am building a 16×20 cabin in Alaska. The plans we had made spec’d rigid foam insulation to be put on the interior as both a vapor barrier and cover the thermal bridging.
The 2×6 wall cavities are filled with R23 Rockwool, then the rigid foam has been applied and meticulously taped. All electrical boxes have been well air sealed with shell boxes and foam. The exterior has metal corrugated siding with tyvek behind it. Everything exterior is fastened to the plywood sheeting.
Is the rigid foam on the interior going to cause wall condensation issues? This is already done – so in reality this is just for mental comfort at this point.
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Replies
There is absolutely nothing wrong with interior rigid foam, since it is on the warm side in cold climate you won't have condensation issues with it.
As you have noted it also doubles as your vapor barrier.
Condensation issues happen if you have a cold side vapor barrier, since both CDX plus house wrap are vapor permeable it won't be an issue. The corrugated siding is also self venting, so it acts as a rain screen to help with drying of any moisture that makes it into the sheathing.