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Dale Nettleton | Posted in Green Building Techniques on

Here’s what I would like to do. I want to install roofing felt, then 2″ pink foam board and cover it all with house wrap. Then install vinyl siding. Can I do this?

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  1. GBA Editor
    Martin Holladay | | #1

    The answer depends on your climate. If you live in a very cold climate, 2 inches of XPS may not be thick enough to keep your wall assembly above the dew point. More information here: Calculating the Minimum Thickness of Rigid Foam Sheathing.

  2. Dale Nettleton | | #2

    I live in zone 4. Thanks for your reply.

  3. David Meiland | | #3

    I don't see the benefit of the foam if it's covered with XPS (pink foam).

  4. Dale Nettleton | | #4

    No currently it is osb. I want to cover the osb with roofing felt then add pink foam then go with a house wrap.

  5. Ron Keagle | | #5


    I don't see the point of the house wrap or the roofing felt if you have a layer of XPS. Regarding the XPS, it should have its joints sealed against vapor passage. Neither the house wrap nor the felt will accomplish that function.

  6. GBA Editor
    Martin Holladay | | #6

    Two inches of foam will work in your climate.

    There are several issues you need to resolve. One issue is: if you decide to install both asphalt felt and housewrap, which of these will be your WRB? You need to choose, because only one of these will be integrated with your window flashing and penetration flashing.

    The second issue is: will you install vertical furring strips over the rigid foam, or will you try to fasten your vinyl siding through the foam with very long fasteners?

    More information on these issues:

    All About Water-Resistive Barriers

    Where Does the Housewrap Go?

    How to Install Rigid Foam Sheathing

    Fastening Furring Strips to a Foam-Sheathed Wall

    Can Vinyl Siding be Applied Over Furring Strips?

  7. GBA Editor
    Martin Holladay | | #7

    Don't forget that building codes require a WRB. Using rigid foam as a WRB is tricky; not all foams are approved for use as a WRB, and it's hard to get the flashing details right.

  8. Ron Keagle | | #8

    Thanks Martin. I see your point and had not considered that.

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