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Window installation details

E247 | Posted in General Questions on

I wanted to get some advice on installing the windows in a house with exterior rigid foam. The walls will be standard wood construction with OSB sheathing. We are going to install 3/4” rigid foam over the OSB sheathing with Tyvek over the foam. A rain screen will be built over the Tyvek using 1 x 4 furring strips for the fiber cement siding. I planned on installing a 2 x 4 flat against the OSB sheathing around the window openings so that the windows will sit flush with the siding and provide a solid surface for nailing the windows. The rigid foam and Tyvek will butt into the side of the 2 x 4. Flashing tape will be installed over the window flange and the 2×4 to the Tyvek. The outside edge of the 2×4 will be flush with the outside edge of the 1 x 4 furring strip so the trim and siding boards can be installed up to the windows. Will this design work? Is there a better/easier way to install the windows?

Climate Zone is 2a, hot humid.

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, can you tell us your name?

    You'll get better thermal performance if you bring your rigid foam right up to the edge of the window rough openings, and then install a "picture frame" of 1x4 furring strips (on the flat) around each rough opening. The picture frame goes on top of the rigid foam.

    Then the window flanges are fastened to the picture frame.

    The method I describe reduces the thermal bridge that occurs with your method (using 2x4s for the picture frame instead of 1x4s on top of the rigid foam).

    For a thorough discussion of your options, see Installing Windows In a Foam-Sheathed Wall.

  2. jberks | | #2

    Make sure you get the window detail from the manufacturer first. I suggest watching out for the windows nailing flange. And what the depth of the window is from the flange to the outside edge of the window frame, See if your furring and siding depths correspond.

    My window guys used the naililed the flange to the window bucks. And then when furring, to picture frame around then window I had to make a special bevel on the backside of the furring to accommodate for the nailing flange.

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