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Community and Q&A

Vapor retarder in cold climate yes/no?

Tia M | Posted in Green Building Techniques on

(Here in south dakota we are not required to follow a code. I can make my walls out of grilled cheese if i so desire)

I’m having a company reside my zone 6a freezing home. its a 1953 ranch house with 2×4 walls. it’s going to be:
Studs with fiberglass batts
osb
2″ of eps
tyvek drain something rainscreen
lp smartside
Builder suggested a vapor barrier that encourages vapor to move to the exterior and not so much inside. I assumed it needs to dry towards the inside easily because of eps? should I drop it, no vapor anything?

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Trina.

    With R-10 continuous exterior insulation on 2x4 walls in Climate Zone 6, you do not need an interior vapor retarder. The painted drywall will do.

    Keep in mind that Tyvek's drainable housewrap is not a true rainscreen. A built ventilated rainscreen detail would make the wall even better.

    Here are two articles that you may find helpful: Walls that Work and All About Rainscreens.

    1. Tia M | | #2

      As far as I understand it the builder is going to be building the rainscreen on that wrap? it's all new to me. and when you say paint will do, oh no I do not intend to paint my walls. they are pretty as is. does that mean I need some form of plastic retarder? I have no idea what kind of paint is on the walls

      1. GBA Editor
        Brian Pontolilo | | #4

        Trina,

        If you have interior drywall that is painted, you don't need to do anything else.

  2. Expert Member
    Akos | | #3

    With that amount of exterior rigid insulation you don't need any interior vapor retarder membrane. Walls that are already painted with standard paint are enough.

    Your installer will need to put on a rain screen over the foam to hang the siding as you can't hang smartside directly through that much foam.

    The rain screen is just vertical strips of plywood or 1x3 lumber installed over the WRB. The siding is then nailed to these strips.

    With this setup you don't need any of the fancier "rain screen" type textured WRB, standard housewrap is good enough. Nothing wrong with using a rain screen type WRB though.

    1. qofmiwok | | #5

      Is full batten rainscreen really required over 2" insulation? I've seen people talk about using long screws to attach through up to 5 and 6" of exterior insulation.

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