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Community and Q&A

Can housewrap be used over rigid foam insulation in climate zone 4?

sN9UCEW4YS | Posted in Green Products and Materials on

I am building a home in climate zone 4 using the Energy Star v3 standards. We are in the design stage.

The walls will be 2 x 6 with 1/2 sheathing and blown cellulose in the stud bays. We plan to use 1/2 inch rigid foam on the exterior of the building to provide a thermal break. The drywall inside will be installed with airtight details specified by Energy Star version 3.

My concern is about the durability of the tape on the rigid foam seams. Wouldn’t a well detailed (and protected) housewrap be more durable than the adhesive of the tape on all those joints? My other concern is would a housewrap over the rigid foam create a moisture trap for vapor ?

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  1. wjrobinson | | #1

    One layer of thin exterior ridged foam is to me not a great design.

    In my area we use two layers. Two layers helps with the fact that the joints in the sheets are trying to leak air.

    Two layers of foam properly taped is better with and the house wrap won't hurt but is not needed.

    And plywood or Zip sheathing or no sheathing is better than plain OSB.

    Watch the GBA YOU TUBE videos too....

  2. Expert Member
    ARMANDO COBO | | #2

    I prefer to use a WRB over the sheathing and then the foam. It makes it easier to install windows properly. In CZ4 you need 1” rigid foam minimum, and depending on your claddings and location, you may want to install a vented screen. (Vented screens are not a good idea in high fire zones and some local codes do not allow them). A layer of rigid foam, taped and sealed, can be a second WRB and an approved tape is as good as the installation, continuous and without creases, bends or knots.
    With closed cell rigid foams on the outside of the wall there will be very little drying of the wall to the outside; installing cellulose in the cavities allows the wall assembly to dry to the inside. The 1" minimum is based on indoors 70°F & 35%RH for most most of CZ4 in the winter.

  3. GBA Editor
    Martin Holladay | | #3

    You can use 1/2-inch foam in your climate zone, but it has a low R-value. Thicker foam would certainly be better.

    Here are the two articles you should read to answer all your questions:

    Where Does the Housewrap Go?

    Using Rigid Foam As a Water-Resistive Barrier

  4. cascadian76 | | #4

    What kind of fam are you planning to use? Why did you choose 1/2 inch?

    I wouldn't think that houswrap over the foam would be a moisture trap...the vapor could dry out the housewrap, or if it's liquid water, drain down the bottom (if the wrap isn't taped at the bottom).

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