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Community and Q&A

Too late for outie windows?

JTyler | Posted in GBA Pro Help on

I framed and wrapped my house planning on innie windows. Walls will be standard construction with 6” exterior foam. Actually…I installed all the windows that way as well. With that behind me, I am feeling like the structural and performance benefits I based this choice on are overblown, and I’d like to change to outie windows. My rough openings are sized for the windows – not the windows plus extensions. I am trying to determine a way to build rough opening extensions that attach outside the sheathing.

My thought is to build boxes of 2x lumber matching the rough openings in size. I would screw 5/8 plywood flanges to the back of these boxes with quality wood screws. These flanges would sit against the sheathing, and I would screw through the flanges and into the king studs, headers, and sill cripples. I would then predrill and send structural screws through the 2x boxes. I am feeling like with care and plenty of good screws, I can build something rugged enough.

Another issue is flashing. Windows are flangeless – currently installed with flexwrap and straightflash. Housewrap is installed, so my drainage plane is in the wrong spot for outie windows. My thought is to wrap these extension boxes in grace ice and water that extends from housewrap to the interior of the house. At the corners, I would use flexwrap or zip stretch tape, installed shingle style. At the heads, I would cut a new flap in the housewrap above the plywood flange, and install ice and water that begins up under that flap.

Is this a reasonable plan? Any potential problems I am not considering or not addressing properly? Any better ideas?

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  1. GBA Editor
    Martin Holladay | | #1

    This is hard to visualize. Some questions:

    1. It sounds like your windows are already installed (as innies). Is this correct?

    2. Have you installed your rigid foam yet?

    3. If your windows are already installed, am I correct that you plan to remove them and re-install them in a new location?

    4. Does your house have a stud wall (presumably, 2x4s or 2x6s) sheathed with OSB or plywood? And then you have installed housewrap on the exterior side of the sheathing as your WRB? Is that correct?

    5. Are you contemplating installing a new WRB on the exterior side of your rigid foam, in conjunction with your plan to move the windows (to make them outies)?

    -- Martin Holladay

  2. JTyler | | #2

    1. Windows are installed as innies.

    2. No foam yet

    3. Plan to remove and reinstall

    4. 2x6 studs with plywood sheathing and drainwrap

    5. I am contemplating installing a new WRB, but currently leaning toward flashing back to the installed drainwrap.

    I am attaching sketchup drawing of planned extensions in case it helps visualize. Thanks as always for your help, Martin.

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like you are going to a lot of work for a small (or illusory) benefit. Are you sure you couldn't just learn to live with innie windows?

    You might get some ideas by reading the GBA article on Dudley boxes. Here is the link: Window Installation Tips for a Deep Energy Retrofit.

    To install these flangeless windows, all you really need is a plywood box. Most builders use 3/4-inch plywood instead of 2-by lumber. Of course, you have to figure out how to attach your plywood box now that the rough openings were framed too small. One possibility is to fasten the plywood boxes (bucks) with 7-inch or 8-inch screws, through pre-drilled holes in the plywood bucks.

    There are lots of ways to do this, as long as you succeed in flashing the rough opening before the windows are installed, and making sure that the sill pan that you install in the rough opening drains to your new WRB.

    Is all this work worth it? Only you can decide.

    -- Martin Holladay

  4. JTyler | | #4

    Would you consider it essential to add a new WRB, or would flashing back to the existing housewrap work?

  5. GBA Editor
    Martin Holladay | | #5

    Flashing back to the original housewrap can work, as long as all of the tricky areas have been thought through.

    -- Martin Holladay

  6. seabornman | | #6

    Why not eliminate the plywood flanges and run some substantial screws directly into the face of the 2x extensions? That's how I plan to build my outie window framing. Those flanges seem to weaken the direct transfer of loads and will be a pain to install foam around.

  7. GBA Editor
    Martin Holladay | | #7

    Your suggestion is the same as mine. I advised that Jim "fasten the plywood boxes (bucks) with 7-inch or 8-inch screws, through pre-drilled holes in the plywood bucks."

    -- Martin Holladay

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