Extra-Deep Interior Windows
briancornwell
| Posted in General Questions on
So we’ve got thick walls with a service cavity. Most of our windows are fixed picture. Our interior sills have plenty of room to fit another window.
– Is there any downside to adding a 2nd window? Aside from not being able to clean the middle glass if it ever got dusty?
– IF cost were no concern.. Could we go crazy and do a triple pane, so in essence double pane (what we have now) + triple pane. Essentially a 5 pane window minus gas in the middle.
Has anyone ever done this, any testing, data, etc?
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The airsealing of both the innie and the outie needs to be flawless, otherwise you'll see condensation in between. There will be convective looping between the series of windows because the air gap is too great, so two double pane windows would not equal the performance of a high-performance quad pane. There are precise calcs and test criteria for selecting the depth of glazing spacers to achieve the optimum balance of reduced radiation, convective and conductive heat exchange. This solution will be far from that optimum. Also the visible light transmittance will be dramatically reduced -- kind of an important feature of windows.
I can say without even doing the math that in all climates the energy savings ROI of this is measured in decades if not centuries.
I'm not sure if this is helpful but I remember staying in a hotel in the Alps, in Austria, seriously cold climate. It had walls about 2 feet thick and had a double (or triple, I don't recall) paned operable window at the outer wall face and another at the inner wall face.