Exterior insulation too thin
Hi! First time here. I recently purchased a new to me home, built in 1979. The previous owner retrofitted a layer of .5” foil faced (foil facing inwards) foam board insulation on the exterior, under the vinyl siding and over the sheathing. There is also house wrap over the sheathing. I am now realizing this was done incorrectly, the foam is not nearly thick enough for our climate zone 6 Maine winters. I know the theory is that it can create condensation problems for the sheathing, but in practice does this really happen? I can’t seem to find anyone actually saying it’s been a problem for them. Fiberglass in the wall cavities, and from what we can tell no interior vapor barrier is present. Time to freak out? Or keep calm and carry on?
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Replies
This is the closet I could find quickly.
https://cwc.ca/design-tools/tool/effectiver/calculator/wall.php?id=2315
Montreal is zone 6, so it seems to work there. Usually you would have faced batts which provides the required warm side vapor control. Also a lot of time the rigid is micro perforated, these even when faced are quite permeable further reducing risk. See if you can figure out which exact rigid you have.
Overall, if you don't see signs of moisture damage in the wall (ie around windows or on the 2nd floor near the top of the wall), I would not sweat it.
Thanks for the reply. No signs of moisture. House was resided and rigid foam added in 2023. Here’s a picture of the rigid foam
That stuff is permeable, you should have no issues.
https://www.buildsite.com/pdf/alliedprivatelabel/TRI-BUILT-EPS-Fan-Fold-Underlayment-Product-Data-1424777.pdf
Hey thank you, very helpful!