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Community and Q&A

Fixing Wrong Window Buck Depth

mpsterner | Posted in Green Building Techniques on

In the flurry of issues this spring with sourcing our Rockwool and answering questions for our carpenters, I sized the depth of our window bucks at the face of our 5″ of Rockwool and not out to the level that our strapping would be set at.

How should I resolve this now that they are ready to install the PVC window extension jambs and trim? Should I overlap strapping ON to the buck or keep it over the Rockwool and there will just be a gap?

You can see how our bucks are set at the depth of the Rockwool in the attached image.

Additionally, should the head flashing just be set on the strapping, behind the siding? Running it back to the wall doesn’t seem very feasible with the layers of Rockwool that would have to be underneath and over and that we don’t know the exact position of the trim until the windows are all set…


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  1. kyle_r | | #1
    1. mpsterner | | #3

      Hey Kyle, It looks like their buck is at the depth of the first rainscreen layer, but then they have a second rainscreen layer too that is done horizontally over the face of the buck. So, do you think that what I am asking maybe doesn't matter then with a waterproof'd buck?

      Should I just let the carpenters from the window bucks with the rainscreen strapping?

      Should I leave above and below the window bucks only vertical strapping and not horizontal?

      Thanks so much.

  2. mpsterner | | #2

    For reference, here is a drawing of what we're doing.

    I am also wondering if the rainscreen underneath the window should have horizontal furring strips or if our exterior trim should only be nailed to vertical rainscreen furring?

    Our builders really want to put on horizontal nailers "framing" each window, but all of the images I find online only have the same vertical rainscreen nailers above and below the windows.

  3. Deleted | | #4


  4. kyle_r | | #5

    In my opinion, it doesn’t matter at the top of the window as you should have z flashing there anyway. At the bottom you could extend the Prosoco onto the horizontal nailer to complete the “sill pan.”

  5. mpsterner | | #6

    Does there need to be a horizontal nailer at the bottom of the window?

    Much of what I see online only has vertical rainscreen nailers up to the window, but there are so few examples with window bucks like this so I am not certain how to handle it.

  6. kyle_r | | #7

    No there does not, I assume your carpenters want to add it for the ease of attaching trim, but it is not needed.

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