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Community and Q&A

ICF & window areas WITHOUT wood bucks

jackofalltrades777 | Posted in Green Building Techniques on

I observed an ICF build that did NOT use wood window bucks for the window areas. They used some temporary wood shoring but once the shoring was removed the window area was all raw concrete and ICF/EPS foam. The windows will be installed directly into the concrete using concrete screws and window brackets. The windows will be installed halfway in the window area or otherwise known as an “innie” window.

This looks like the better alternative to window installs on an ICF home and it is common practice in Europe on masonry homes. I am NOT a fan of treated wood within the concrete window buck area. The potential for rot, termites (still possible with treated wood), warping and twisting, etc. Anchoring the window directly into the concrete and having no wood seems like the better route.

Anyone else see this type of build-up/detail? Any potential issues?

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  1. GBA Editor
    Martin Holladay | | #1

    The first step would be to check with the ICF manufacturer to learn whether your proposed installation detail meets the manufacturer's recommendations. If it doesn't, at least you know that any risks are on your shoulders.

    I see no reason why your proposed method wouldn't work, as long as you choose windows that have jambs that can be secured with screws, and as long as you don't mind looking at (or plugging) the screw heads.

    You had better be 100% sure of your detail before you get in too deep, however, because once you choose a rough opening size, you will find it difficult to make the R.O. bigger.

    If you are installing windows as in-betweenies, remember that you will need a flashing detail for the sill -- a detail that covers the exterior EPS at the sill.

  2. jackofalltrades777 | | #2


    The ICF manufacturers don't really say one way or the other. They leave it upon the window manufacturer.

    The windows would be installed via screws threw the jambs (with screw covers) or using brackets that lock into the sides of the window frames and then the other end of the brackets screw into the 6" concrete core.

    The flashing is an impermeable peel and stick membrane that adheres to the ESP and the other side of the peel and stick membrane has a polyester surface which you can then apply EIFS to.

  3. Stephen Thwaites | | #3


    I'd be cautious about the thermal effect of installing directly on the concrete.
    A wood buck does have some drawbacks. However, it does help reduce the bypass losses associated with a “middie” in ICF.

    Not sure of your exact situation, but the attached dwgs from an existing file to show the thermal impact of going 'buckless' for one situation.
    In the top right dwg, the isotherms for the buckless install'n show there is a spot between frame and jamb extension that is colder than the edge of glass (about 8F cooler)
    The same spot in the lower right dwg is warmer than the edge of glass. (about 2F warmer)

    Perhaps you could consider some other material for the buck, like foamed/cellular PVC or a high density foam insulation. A layer of insulation between the roomside jamb extension and the RO would also help reduce bypass losses.

    Hope that helps.

    Stephen Thwaites
    Thermotech Fiberglass Fenestration

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