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Housewrap/Drainage Plane Behind Fiberfaced Polyiso or in Front?

cloves2016 | Posted in Green Building Techniques on

Hi everyone,

I am about to begin residing my house. I was wondering what everyone’s input was on where the housewrap should go in this case.

House is located in North NJ (zone 5-6 border).

-Framing is 2×4
-Fiberglass Batt Insulation R-13 in studs
-Polyiso 1.5″ (fiberglass faced polyisocyanurate)(permeability <1.0) less than 1.0 according to a buildingscience article. Design & Construction Option 1: -Vinyl Siding -Polyiso 1.5″ (permeability <1.0) -Housewrap (Tyvek or Dow)(Drainage Plane) -1/2″ Plywood -2×4 Studs (Fiberglass Batt Insulation R13) Design & Construction Option 2: -Vinyl Siding -Housewrap (Tyvek or Dow)(Drainage Plane) -Polyiso 1.5″ (permeability <1.0) -1/2″ Plywood -2×4 Studs (Fiberglass Batt Insulation R13) I am still a bit unsure of where the housewrap/drainage plane should be in my particular situation. Thoughts/comments?

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, I'd like to distinguish between a water-resistant barrier (WRB) and a drainage plane. In your case, the housewrap is a WRB, but it doesn't sound like it will be a drainage plane. It won't be a drainage plane unless you include an air gap. That can be accomplished many ways; one way is to include a three-dimensional plastic mat like Cedar Breather.

    If you want a true drainage plane, it should ALWAYS go on the outside of the rigid foam, because you don't want any air movement between the exterior insulation and the cavity insulation.

    If you are just talking about your WRB, it can go in either location. Just remember: your WRB has to be integrated with your window and door flashing, so think through your flashing details before you make your decision. Here is an article to guide you: Where Does the Housewrap Go?

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