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EPS unfaced type 1 or R-tech?

SouthDakotaRoof | Posted in Green Building Techniques on

I’m in south dakota zone 6a. I’m having exterior insulation then a rainscreen retrofitted over r13 FG in my walls with taped zip sheathing. I confused myself by reading too much. Tomorrow is insulation day and my last shot to change anything. I have 2″ unfaced eps which seems like it might have been meant for below foundation use (sku: 1632118 on the Menards website),
*I’m worried R-tech might be the better option but it has a laminated polymeric facer on it?*
I dont have any vapor barrier/retarder other than latex paint.
*I want my exterior walls to be vapor open, I think, so I should stick with the current unfaced option? *
And slightly off topic question, I’m about to renovate the bathroom and I assume it should have a stronger vapor retarder than just paint,what do you suggest?

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  1. Expert Member
    BILL WICHERS | | #1

    That sku is type I unfaced EPS. It’s fairly crumbly. I’ve used that exact stuff for some work insulating my rim joists. You’ll want to cut it with a hot wire cutter, anything else will make a mess of things.

    Menards now stocks what they’re calling “high density” EPS. It costs more, but it’s much easier to work with. If you have a lot of cuts to make, this higher density (likely type II) EPS will be easier to work with. You could use the cheap stuff where you’re using full sheets and the more expensive stuff in areas where you have detailed cuts to make (like around windows).

    Faced EPS is easier to handle, but typically is a vapor barrier due to the facer (unless it’s a perforated facer). I think you’d find this easier to use, but then your wall would only be able to dry to the interior — which probably isn’t a problem.

    Personally, I’d use polyiso here for maximum R value and I wouldn’t worry about it being vapor closed. Just don’t use vinyl wall paper or other vapor barrier wall coverings on the interior and you’ll be ok.


  2. Expert Member
    Akos | | #2

    You generally want unfaced product for walls. 2" EPS is still fairly permeable, it is excellent insulation for your application. You'll have a well insulated and robust wall. Going to polyiso does increase the R value a bit, but also your cost. Unless you are in very cold climates or your heating fuel is expensive, I doubt it is worth the cost.

    Pretty much the only issue with it is what Bill brought up. It does make a bit of a mess when cutting. Hot wire is nice, but I doubt any trade will have one. Just be ready to clean up after the crew.

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