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Community and Q&A

Window flashing

John Waller | Posted in GBA Pro Help on

What is window flashing detail for board and batten?
2×6 stud/plywood sheathing/tyvek/1” exp foam/3/4 furring strip/smartside vertical B&B siding. Should  I will fasten vinyl window flange to wood frame in plane with outside of foam or inside?

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  1. Expert Member
    Malcolm Taylor | | #1


    If you are putting the WRB (the Tyvek) behind the foam, the window should go there too. If you want to mount the window on the f0am you should move the WRB out as well.

    One thing to look out for is that if the windows you select don't have enough depth on the outside of the flange, they may not cover both the foam, furring strips, and boards. That will complicate the window trim.

  2. John Waller | | #2

    Ok. I will place window flange flush with outside of foam. And use the foam as the WRB

    1. Expert Member
      Malcolm Taylor | | #3


      The advantage of moving the Tyvek out and keeping it as your WRB is that you can lap and flash the windows as you usually do. If the window is mounted directly to the foam you have to rely on taping the head and jambs - and have to tape the seams of the foam.

  3. GBA Editor
    Peter Yost | | #4

    Hi John -

    If you install the window in plane with your exterior rigid insulation, just make sure you follow what is required by window manufacturer in terms of how much of the window needs to bear on supporting material (i.e framing).


  4. Expert Member
    Michael Maines | | #5

    You might want to check out this product, made for this situation:

    1. Brendan Albano | | #6

      With only 1" of exterior foam, is there an advantage to using the ThermalBucks vs just screwing the flanges through the foam into the wall like Building Science Corporation often recommends for foam up to 1 1/2"?

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