Third glass to old windows (quick and cheap)

If you’re planning to upgrade from triple glass windows to modern argon filled selective glass window modules, your investment may never pay itself back. However moving from double glass windows to triple glass windows or better saves more energy and payback time is shorter.

In our case destroying the historically valuable windows by moving to modern window modules was out of the question. I could have added window modules between the outer and inner glass but that would have been expensive, since every window has multiple screens: three or six. Every screen would have required its’ own module. The modules would not have been invisible either and could have spoiled the historical looks of the windows.

Still, double glazed windows do condensate a lot of water during fall and early winter when the temperature is going down and the relative humidity inside is still high. It’s a drag to wipe them every morning.

So I ran a little test: I added a third glass on the outside of the inner window frame last winter. That reduced the condensation a lot. There was only a little condensation at the lower edge on the most extreme low temperature days (I think we had something like -35 C degrees here). It evaporated by itself during the day.

Recently I added a third glass to every window we have. I cut the glass myself from the windows we had gathered from various sources, so the glass itself was free. I attached the glass with small strips of thin sheet metal that could be bent with fingers. I punched holes to the other end of the strips and screwed them to the window frames. I sealed the gap between the frame and glass with P-profile window seal (P-profile allows a bigger gap). Note that you may have to leave gaps in the seal if you see condensation between the inner and middle glass (only the inner seal must not have gaps). The attaching points of the metal strips leave naturally small air channels, so I haven’t left any gaps, but haven’t seen condensation either.

The whole job, dismantling the gathered windows, cutting glass, making the metal strips, cleaning the windows (and scraping of spilled paint drops: I hadn’t done this earlier) and attaching the glasses took six days. That’s for 46 screens. But I believe most of the time was used in cleaning the windows. The whole thing cost only 83 euros for the 200 meters of window seal. I think the payback time will be short.

The third glass is also almost invisible from inside. Only if you look from a steep angle, you can see the metal strips. From outside you rarely pay attention on the inside frame, plus often you have reflections to block the view anyway, or it’s too dark.

Here’s some pictures:


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