Flangeless Windows Done Right
Learn how to install European-style windows that sit within the rough opening and require a face-sealed approach to water and air management.
Synopsis: Flangeless windows, often referred to as “Euro-style windows,” have different installation details than the flanged windows common in the United States. In this article, builder and remodeler Jake Bruton details a Flangeless window installation: locating the window in the opening, flashing the rough opening, setting and securing the window, and then face-sealing for water and moisture control.
Some of you may have taken the time to watch my video series with Fine Homebuilding about properly installing flanged windows in multiple assemblies. Those methods apply to most windows installed in the United States, but they don’t apply to flangeless “European style” windows, including the triple-glazed, tilt/turn windows preferred by many high-performance builders. This type of install is known as a “face-sealed system”.
Of course, some of the fundamental principles are the same; shingle-style lapping, for example, is the right way to detail any window flashing, as well as using a back dam and creating a slope at the sill of the rough opening. Your walls may vary, but these principles will provide a solid starting point so that you can adapt the installation to suit your situation. The windows on the project shown here are from Schüco, though many European-style windows install similarly.
Locating the window in the opening
Over the past five years I have not built a home with walls that were less than 71⁄2 in. thick. Most of the time that assembly includes 2×6 framing (51⁄2 in.) plus 1⁄2 in. of drywall inside and 11⁄2 in. of Zip System R-sheathing outside. Having this thick wall gives us an opportunity to make choices about how our Euro-style, flangeless windows are installed.
One option is to push the window outward in the assembly, but this presents more challenges for water management because the window is closer to the weather. Moving the unit to the interior face of the wall better protects the unit from the elements, but in doing so, also moves the unit away from the sunlight and the breeze—two reasons why we have windows in our houses in the first place.
The other factor that must be considered when positioning a window unit is the potential for creating a microclimate. If the window is placed all the way to one side within a deep wall (in this case, likely deeper than 71⁄2 in.), you limit airflow in the window well on the opposite side, and this raises the risk of creating a zone that is different than the surrounding areas. This microclimate can create the right conditions for moisture accumulation in areas where you don’t want it. For this reason, I typically locate the window in the middle.
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More about window flashing:
Don’t Forget the Flashing – Easily overlooked and sometimes installed incorrectly, flashing keeps water out and rot at bay.
Flashing for Old Windows – How do you get a good weathertight seal on old windows that don’t have a flange?
Fix for Poorly Installed Window Flashing – When water is leaking in around newly installed windows, chances are that there are some missing or improper flashing details that need to be corrected.