GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X 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

Nail fin windows and 4″ of foam

DIYJester | Posted in Energy Efficiency and Durability on

I installed the first of my new windows today in the wall with 4″ of foam. I set it up as an outie with a 3/4″ plywood buck/box to hold the window. I have 3/4″ furring around the window. The buck/box is securely fastened to the rough out.

I used 6″ screws with plastic washers in the nail fins to studs (mostly) at the corners and midpoints. I used ring shanked nails in the rest of the holes into the furring.

Does anyone see this as being a structural issue? I couldn’t push the window out by hand any noticeable amount, but I am installing 4 4’x6′ windows in a similar fashion which are much larger. These may have my dogs, and possibly future children pressing against them. I could easily use staples around the nail fin to ensure it is stuck to the buck also if this would help at all.

So far I am very impressed with the new window minus the weight and the slight differences in visible light. The visible light portion is something I should have expected going from a dual pane clear glass to a triple pane cardinal 366/clear/366. The 4’x6′ windows will only be double pane due to their size.

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. GBA Editor
    Martin Holladay | | #1

    If the flanged window is attached to your "picture frame" of 3/4-inch-thick furring, then the security of the attachment depends in part on how securely the picture frame is screwed back to the framing. Make sure that the picture frame has plenty of screws (but not so many screws that the wood starts splitting).

    For more information, see Installing Windows In a Foam-Sheathed Wall.

  2. DIYJester | | #2

    Thanks for the response. I predrilled and countersunk the 6" screws to help with the splitting and haven't had that issue. I trust the furring strips to support my weight so all should be well. The biggest pain so far has been detailing the wrb around my "picture" frame.

  3. Reid Baldwin | | #3


    I am pleased that you are posting about what is working well and what is a pain. I am still deciding what method to use for mounting the windows in my walls which will have exterior foam. I have read a number of articles about the alternatives including the article mentioned above by Martin. Is your WRB at the surface of the foam or at the sheathing?

  4. DIYJester | | #4

    My WRB is at the surface of the foam. My wife wanted the larger window sills so outies it was. Unfortunately (as far as detailing) my doors will be innies as I don't want to cantilever the doors over Roxul (below grade).

    For the side of my house with no windows/doors, I used short staples to temporarily hold the WRB to the foam. I then put up the furring strips. For the window opening this is not as easy because I have to have the furring up before the window, which means the WRB is behind the furring and window flange.

  5. Reid Baldwin | | #5

    Apparently you used a housewrap as the WRB. Did you use a type of foam that isn't qualified as a WRB or did you just feel better about housewrap than about tape?

  6. DIYJester | | #6

    I felt a bit more comfortable with a house wrap just in case code officials got involved. The house had no WRB initially, but for some reason they did cover the attached garage... with this builder though I may never know why.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |