GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Peel & stick – Under or over the strapping

user-1066984 | Posted in General Questions on

I’m in the process of building a thick foam covered wood framed house.
It’s a 2×6 wall with 2.5″ of XPS, followed with 1.5″ of polyiso foil faced and taped. In order for me to apply my vinyl siding i need to add 1×4 strapping and 2×10 windowbucks as the foam is so thick

I’m uncertain on whether of not to put the peel and stick membane over the 1×4 strapping or under?
My windows are new contruction and have nailing flanges

I have included a picture of what is going on… if i go over the 1×4
you will have to imagine the green membrane under the 1×4 of the other option, but i think you can all see what i’m after.

I was planning caulking the nailing flange and then adding a peel and stick over top of the nailing flage as well

Is this correct?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. tmtrainor | | #1


    The best location for the membrane is under the insulation layer. See how Joe Lstiburek designed his Barn:


  2. user-1087436 | | #2

    I'm not one of the experts, but according to the videos and blogs I've seen hereabouts, a 2x10 buck is way oversized. A builder in one video says 3/8" plywood is sufficient. Martin Holladay says to use 3/4" plywood. A 2x10 seems like a huge thermal defect. I hope I'm not speaking out of place to say this, but that's the way it looks to me. Your numbers also don't seem to add up. A 2x10 is 9 1/4" wide, and you've got 9 1/2" of foam and wood above it. Look around the site more, and I think you'll find ready-made drawings that will suit you.

  3. user-1066984 | | #3

    Hello everyone, this is not something I think I'm doing, it's already done.
    Just the window bucks and strapping need to be installed....very soon

    I used 2x10 material as some of my windows are 8 ft wide and was concerned for weight of window over time...

    The 1/4" gap that Gordon mentions will be made up, on the inside before drywall

  4. GBA Editor
    Martin Holladay | | #4

    Before we can answer your question, we need to know where your water-resistive barrier (WRB) is.

    WRBs are required by code. You can use asphalt felt, plastic housewrap, or rigid foam as your WRB. However, if you use rigid foam as your WRB, you have to follow the exact details provided by the manufacturer of the rigid foam. For more information, see Using Rigid Foam As a Water-Resistive Barrier.

  5. user-1066984 | | #5

    The last foam layer (ISO) is my WRB. I was going to use a traditional WRB like typar or somethign of the like, but cannot figure out how to integrate the at the window head...just like my diagram above.

    If i use a traditional WRB, it would have to go under the strapping, how to you integrate in with the window head and nailing fin on window?

  6. GBA Editor
    Martin Holladay | | #6

    If you are using rigid foam as a WRB, you have to look up the recommendations of the foam manufacturer (and incidentally, you have to verify that the type of foam you purchased has been approved for use as a WRB). Once you've looked those up, you have to follow their recommendations to a T -- or you won't be code-approved.

    At this point in time, the only methods approved for flashing rigid foam used as a WRB depend on tape, not gravity or laps. You must use the type of tape recommended by the manufacturer of the rigid foam.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |