Can I replace this window with a sheet of double pane glass?

September 25, 2019 5:56 AM

I would like to replace a "storm" window with double pane glass. Can it be done? (More info and a picture inside.)

I would like to replace the entire removable wood-framed window (outlined by black arrows in the picture) with a piece of double pane glass, more-or-less permanently put into the wood ("outside of the arrows"). I do not just want to replace the glass in the frame, but replace everything, frame and all, with just a window. I would plan to caulk or weather-strip it in, and tack on a wood molding (painted to match) to anchor the glass to wood of the house. I live in the north; cold winters.

Advantages should be more light (the frame is 2 inches around three sides, with a four inch width at the bottom), and better insulation. (Also I would not have to scrape and re-paint the frame.) I would have a window place make the glass pane.

What problems do you foresee? Any tips on how I should do this?

posted by mbarryf to Home & Garden (9 answers total)

Sure. You can order a custom piece of double or triple pane the correct size at a good glass shop. Go triple for better insulation. Specify low-E if you want to reduce solar gain in the summer. When you have the old window out, squirt expanding foam into any cavities around the frame that are exposed. Use sturdy molding, not just caulk, to hold it in place.
posted by beagle at 6:08 AM on September 25, 2019

So, you want a storm window but you want it to have less frame or no frame?
posted by amanda at 6:11 AM on September 25, 2019

For my answer above, I understood this to mean the whole window (both what looks like a wooden storm and the inner window) comes out, and a non-operable double pane goes replaces it. You can do that, but I would not replace just the wood-framed storm window with a sealed double pane unit, because without some weep holes for drainage you are likely to get condensation on the inside surface of the double pane unit. So to avoid that I recommend taking the whole window out and replacing it with the double or triple pane unit.
posted by beagle at 7:30 AM on September 25, 2019

Response by poster: To amanda. The "storm" window is an exterior window that can be removed, but we never remove it, as the interior side of that window cannot open. I want to replace that wood-framed window with something permanent, and more energy efficient. The smaller frame would give us more light.
posted by mbarryf at 7:37 AM on September 25, 2019

You can get double-paned glass made to order; I have to do this for a window where only 1 pane broke. The wood is an adequate insulator, so I would just replace the glass, I would prefer this aesthetically. Talk to a goodgreen builder about sealing the window in place; moisture can get trapped and will cause rot if it does.
posted by theora55 at 9:33 AM on September 25, 2019 [1 favorite]

Contrary to popular opinion, windows account for only about 10% of energy loss in a typical home, and most of that comes not from conduction through the glass itself, but from infiltration of air around the sash. The energy efficiency you will get by replacing this one window will be minuscule and unlikely to pay for itself in the long run. Your light gain is also likely to be marginal.

The installation of a double-glazed unit directly into the window pocket also comes with risks. I'm assuming you will be using some kind of structural silicone glazing and installing a stop (caulk or weatherstripping is not going to do it). We've dealt with the aftereffects of this on a large project where glass was installed directly into the frame as a temporary measure, and trying to remove the glass to install operable windows has actually resulted in damage to the window jambs . As theora55 notes, if any water infiltrates, it can cause deterioration of the jamb. In both cases it is much harder (and more expensive) to replace the jamb than a sash. You will need to have very precise measurements for the glass so it fits in the pocket. Are you sure the frame is plumb all around? If it isn't, it could be difficult to fit the glass in.

Window sash are designed to have some give. Especially in an older house (which I suspect you have) there is typically some movement, and any racking of the jamb could transfer into the glass and possibly break it.

For comfort and efficiency, you'd get better results by replacing the current single pane storm with an insulated unit...it will go far beyond what you have now and will be quieter to boot.

Be very careful with the use of expanding foam. High expansion foam (what you typically get at a home improvement store) will press against the windows and can break the glass and/or rack the jamb. If you do this, get a closed cell, low-rise expanding foam - one brand is called "Great Stuff".
posted by Preserver at 9:50 AM on September 25, 2019 [6 favorites]

One potential problem would be moisture and cold air getting between the panes of glass. When a manufacturer joins two panes of glass, they replace the air between them with some type of gas (some gases have better insulation/resistance value than straight room air). When that seal leaks, the window steams up. Maybe instead buy a commercial replacement window pane that has already been sealed in this way?
posted by summerstorm at 9:51 AM on September 25, 2019

Not all double pane units use argon in the airspace. It's an up charge, and it's only worthwhile in the north. It slows radiation from interior to exterior.
Here in the south, dessicated air has a more economical life cycle cost.

There are no weeps in the glass unit itself. Those are provided in the frame. The glass unit is, and must be, hermetically sealed or it will fog.
I'm with those above thinking this might not be the best idea - condensation behind the glass, possible structural movement, etc. You are quite likely to get condensation on the interior face of this glass, the water will then drain to the wood window sill, you'll have no way to get in there and maintain it, the sill will then rot.
posted by rudd135 at 6:09 PM on September 25, 2019

I agree with Preserver. If you are primarily concerned with insulation, your proposed solution might not make a measurable difference. Storm windows, particularly with wood frames, are actually pretty good insulators. If you do not have condensation or ice on the living room side of the window on the coldest days in winter, your storm window is doing a good job.

You might be better off putting your money and effort into other insulation strategies such as weather stripping for air leaks and roof or attic or wall insulation.
posted by JackFlash at 6:28 PM on September 25, 2019