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  1. user-2310254 | | #1

    Justin,

    I will give you a bump. It's good you are being careful and asking questions since stucco is a reservoir cladding. Do you know if the sheathing is covered with builders felt and if it is intact?

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  2. Expert Member
    PETER G ENGLE PE | | #3

    There are some threads here at GBA on how to insulate a wall with no sheathing. Some of these techniques might help. If your felt paper is not 100% waterproof, it would be a good idea to have some sort of air gap/drainage material between the backside of your cladding and the insulation. Does your local code actually require you to bring your insulation up to R-20 in an existing building? Many jurisdictions just say to fill the cavities the best you can. That makes a difference. Still, with 5" or so to work with, R20 is achievable.

    You can install a "smart" vapor retarder on the interior to protect the wood framing from condensation. I'm not sure that is even necessary in your dry climate, but it would provide some extra protection. Depending on your level of gutting, an interior vapor retarder can also be an effective air barrier without much extra effort. You need to pay attention to the following issues, in order of importance:
    1. Bulk water
    2. Air leakage
    3. Insulation
    4. Water vapor

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  3. Expert Member
    AKOS TOTH | | #5

    Old stucco install generally missing a couple of key water management details, this generally means insulating with batts only can cause issues down the road.

    The simplest is to assume that water will make it through the stucco and board sheathing and insulate accordingly.

    Since you are in pretty dry climate, closed cell SPF would probably work. If you don't want SPF you can insulate with batts provided you follow the details here:
    https://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing

    Dimple mat is a vapor barrier, which is generally a bad idea in a climate with a lot of heating. The better option in your case would be grooved EPS. Unfaced EPS is permeable and will allow moisture transfer through the wall. This is sometimes sold by box stores as foundation insulation or available from EIFS suppliers.

    P.S. 50% RH in the winter is very high and rough on building assemblies and might cause condensation on windows, you won't get static issues unless you go bellow 30%.

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