More Energy-Smart Details
This detail was used on a new-construction project that was pursuing Passive House certification and net zero–energy performance. The double-stud wall system has 2×6 exterior load-bearing framing 24 in. o.c. and 2×4 non-load-bearing framing 24 in. o.c. to the interior. A 3-in. cavity between makes for a 12-in. wall assembly.
The aluminum-framed triple-glazed windows are flangeless, which means they could have been installed anywhere within the 12-in. wall. In most high-performance homes, windows are installed in the center third of the wall. This is our preferred location because if the window is pushed too far toward the exterior of the wall—a colder location—the window cavity has the potential to become a microclimate that could lead to condensation problems; and if a window is pushed too far inward, it becomes difficult to manage water at the exterior sill.
That said, almost all our clients want a deeper interior stool, which is among the reasons we installed this window closer to the exterior. The main reason was that it was an exceptionally large window, which we handled with a triple-LVL header on the exterior wall. The interior drywall extends into the window cavity creating a 10-in. window stool.
Here, the center of the window frame is out about 9 in., which is the beginning edge of the outer third of the wall. If we brought the window closer to the interior wall, we would need to add blocking and would lose the full value of the double-stud wall’s thermal break. Also, the window-fastening system relies on metal clips rotated into the aluminum frame and screwed to the wood frame, as shown. By installing the window closer to the exterior framing, we can easily screw the metal clip into the 2×6 wall.
This location, which puts the window roughly 1 in. inboard of…
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6 Comments
The 5/4 head presumably continues right around the window. I'm curious as to what it attaches to and how?
I was curious about 5/4 head also?
What is the climate Zone? Was curious because it seems like very wet climates like the Pacific Northwest stay away from a double stud, but in Mountain states which are very dry this detail is more typical. Any thoughts?
Did you consider either rigid foam board insulation with intermittent blocking at clips or use of high compression value thermal blocks (such as Armatherm 500) in lieu of 2 x 6 framing? What I also noticed is a lack of space for differential movement and construction tolerance at the head, and that SPF sealant between sheathing and framing is useless inboard of the air barrier (Zip sheathing to transition tape with sealant around window frame).
I insalled triple glazed flangeless all fibreglass Alpen windows in 8in Nudura ICF walls. I adapted a product called ThermalBuck for continuous 2in insulation around the entire perimeter. I aligned the windows flush with the extrnal surface of the ICF forms so they will effectively be recessed by the thickness of the siding structure - about 1.75 in. I am installing extended window stools for window seats. I will upload the detail drawing if anyone is interested.
I find Alexandra's articles interesting and informative and have used some of the techniques and details is my build. Sadly, she rarely, if ever, circles back to answer questions. I use them as articles in JLC or Fine Homebuilding, but it would be great discussion if she could join in.
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