At the glass repair company where I work in Philadelphia, Pennsylvania, at least once a week we get a call from a business or homeowner with a broken double-pane window who asks us if we can replace it with just a single pane of glass.

Why in the world, you ask, would someone want to replace a double-pane window with a single pane? There are two reasons for this. One is the time factor. Double-pane windows (also referred to as a thermal or insulated windows) have to be custom-ordered and typically take between five and ten working days to be manufactured, whereas installing a single pane into the opening is something that can be done that very same day. The other reason is cost. As one would imagine, a double-pane window is more expensive. After all, a single pane of glass is just that. Conversely, a thermal window, in addition to obviously having two panes of glass, also has quite a bit of technology built into it. And technology isn’t cheap. Replacing a large double-pane windows can be a significant expense.

As far as the actual job is concerned, converting a commercial double-pane window to a single pane is a relatively simple matter. For modern storefront glazing (known as “flush-glaze”) manufacturers sell a simple converter system that drops into the existing frame and re-configures it to a single-glazing width. Converting a residential window, however, is a different story. Residential frames and sashes are designed to hold a double-pane window (known as a “unit”) of a very specific thickness, and due to the proprietary nature of residential windows and no doubt a general lack of demand, there exists no converter system for this task. But that doesn’t mean it can’t be done. And done well, at that.

On a fairly regular basis I come across a homeowner or, more typically, an apartment dweller who, for one reason or another absolutely insists that they need to have their double-pane window repaired that very same day. It is for these customers I have developed the following method for doing such a repair, the result of which is semi-permanent (it can be easily reversed), and has an air-tight, water-tight seal.

After removing and disassembling the sash, then de-glazing the old thermal unit, a single piece of plate glass with a thickness of 3/16 or 1/4 inch (as opposed to the two pieces of 5/32 inch glass which is usually found in residential thermal windows) is cut to a size that fits snugly into the sash and is laid flat in a continuous bead of silicone on the inside of the exterior side of the frame. 1/16th inch thick neoprene setting blocks are then wedged along the edge of the glass, two per side. These act as a very effective shock absorber between the glass and the sash, and keep the pane from moving in any direction.

Next, a second bead of silicone is laid around the edge of the interior side of the glass. Finally, a number of carefully-sized small wood blocks (typically two or three for each side) are wedged between the interior side of the sash and the glass, forcing the pane snugly up against the exterior side of the sash.At this point the window is then re-installed. After the silicone cures in 72 hours, the customer pulls out the wood blocks and it’s done.

I’ve been doing this type of window repair for almost 15 years and have never had a single call-back or complaint. There are, however, two caveats that must be explained to the customer before I agree to do the job. The first is obvious – that they lose the thermal properties of having a double-pane window. The second is that, while the window will look the same from the outside, there will in fact be a gap of a 1/2 to 3/4 inch inside the sash. After all, if you put a 1/4 piece of glass into an opening that measures 7/8 of an inch, you still have a 5/8 inch difference. As it is, the inside of the sash is the same color as the outside, so the visual difference is negligible.

And there you have it.