Foil-Faced vs. Unfaced EPS
rldev
| Posted in General Questions on
I plan on using eps board for rafter vent baffles. I will seal in the eps with closed cell foam, Does it matter if the eps is foil faced or unfaced? Foil/Poly faced is cheaper. Rock wool will be installed in the rest of the cavity.
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Replies
No, not for just the baffles.
So you are saying it doesn't matter? Thanks for the reply.
That was my intent, I'm short on words today!
Hahaha. Thanks again.
For a bit more nuance: ideally the EPS would be unfaced, because then it's vapor permeable and any moisture that makes its way to the baffle can get to the vent space relatively unimpeded. But very little moisture should be getting there, and what does get there will move through the rafter without causing damage; in that case, an impermeable facing is fine. But I would be careful about sealing the interior from air leaks and would consider a variable permeance vapor control membrane.
Thank you. Can you recommend a control membrane?
Certainteed's Membrain is a good choice if you want reasonable performance and minimal cost. Intello is a good choice if you want better performance and you're willing to pay more for the product. I've usually just used Membrain in these kinds of places where the vapor retarder is just there for extra insurance and is not a critical part of the assembly.
Bill
I specify Siga Majrex or Pro Clima Intello, and also just used a Rothoblaas product on a recent project with good results. Certainteed Membrain also works and costs half as much as the others, but it's also more vapor-open so it's somewhat less effective. Like Bill says, this is a pretty forgiving application so the highest performance may not be necessary.
Thanks for all the suggestions.