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Replacement windows with no frames!

user-7527051 | Posted in GBA Pro Help on

1. How would a flange-less, replacement window get flashed to a plywood buck?

2. I know windows can install with masonry clips to jack studs, but can a flange-less replacement window…and still get properly flashed to the WRB (in my case 1 1/2″ Dow XPS)? 

Brand new (2018) Kohltech triple pane REPLACEMENT windows (no flanges) installed in existing (1995) Anderson Narroline PVC-wood core frames. Wood core frame is saturated. Replacement windows removed. Anderson frames removed. Rough opening exposed. No flashing (this was the job of the Anderson frames). 1 1/2″ Dow XPS foam (WRB) over sealed OSB sheathing (air barrier). 2×6 stud cavity 24 OC with HD fiberglass.

I have a solid building science background and read MANY GBA articles, but this one in particular is good:

Question Details:
The Anderson frames provided an integrated sill. Now that the frames are gone, I have replacement windows with no sill. I want to install these windows with as few parts as necessary and decided to go Outtie with a picture frame casement trim finish.

The article section “Outtie Window with a Plywood Buck” notes “Install peel-and-stick flashing to the sides and top of the window; flashing should overlap the window flanges (if any)…” These replacement windows do not have flanges. How would a flange-less window get flashed to a plywood buck?

Alternatively, I can get nailing fins from Kohltech for these replacement windows. That would solve “how to fasten the window to the WRB” issue and may be less labor than window bucks.

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  1. Boring19 | | #1

    Not sure if this helps, I was kind of in the same boat.
    I built Dudley boxes, I added two inches of foam to the wall.
    The windows were 7 years old non flanged vinyl in great condition, but the frames were toast.
    I slanted the bottom of the box for drainage and used liquid flashing from prosoco.
    My windows screws through the sides and foam around the window to the box.

    1. user-7527051 | | #3

      Gregory, I get your install procedure. If you're flashing the Dudley box to the WRB, what about the transition from the flashed box to the window? How does this get sealed?

  2. Expert Member

    Mike Maines, and a bunch of other high performance builders around him in New England, install flange-less windows in most of their projects. Hopefully he will chime in.

  3. GBA Editor
    Brian Pontolilo | | #4

    Hi Brian,

    I would imagine that your flashing details would be similar to the way Steve Baczek and crew installed the windows featured in this article, except that with the window out at the edge of the buck, you may need to lap your flashing tape onto the face of the window and cover it with your trim. Here's the article:

    Also, if you add flanges, you may want to take some steps to make sure that the flanges are watertight, similar to what Mike Guertin discusses in this video:

    1. user-7527051 | | #5

      Hi Brian,
      Thanks for the response. I read the first article. I would be concerned about tape to PVC window frame is not resilient, especially for the gable walls that I'm working on - they take the brunt of the elements. Also, hiding the tape edge with too keen on that. I've been able to source nailing fins from Kohltech, so that solves the Flange-less problem!

      Trim detail: I'm considering cutting back the siding about an 1", securing the nailing fin with a 2" exterior screw through the 1 1/2" XPS foam into the wall framing, flashing the fins, installing Azek trim with a 1" face showing as finish same as the nailing fin - through foam into wall stud - and finishing the trim to the edge of the Azek.... the issue could be securing the edge of the siding....Thoughts?

      1. GBA Editor
        Brian Pontolilo | | #6

        I'm not sure what the concern is with the ends of the siding. Nailing?

      2. jameshowison | | #10

        There might be some interesting elements for you in this article, Particularly the "Zero-Reveal-Taping" (although sounds like you are going with nailing fins).

  4. user-7527051 | | #7

    Correct, nailing the ends of the siding. Maybe my head is exploding with TMI, but is the procedure as simple as this high level view?
    1. flash window to 1 1/2" XPS and secure with appropriate screws into wall stud
    2. install 1" x 4" nailer over flashed window with same screws into wall stud
    3. install trim secure to nailer
    4. install siding secure to nailer

    Thanks! Brian

  5. Boring19 | | #8

    My windows were set in place, shimmed and screws installed snug, foam around the window from the inside. Prosoco joint and seam sealed filling the gap around the window exterior, followed by a coat of fast flash.

  6. GBA Editor
    Brian Pontolilo | | #9


    The only concern I see there is flashing the window to the foam. That's fine if the foam is your WRB. If it is, it should be rated for that use, all seams taped, etc. Often, the WRB is the housewrap installed between the foam and the sheathing.

    Also, be very careful when cutting the siding back to make sure that you cut straight and square or installing the new trim will not go smoothly. You can attach a shooting board to the house and use a circular saw to make the cut.

  7. Boring19 | | #11

    Hello Brian, yes were using foil faced rigid insulation foam r max with taped seams and staggered joints for the WRB.

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