How To Repair a Double-Pane Window

Double-paned windows are all about efficiency. These glass assemblies feature two panes of glass sandwiched over a metal spacer frame and sealed around the edges. Between the panes is an inert gas, usually argon, that prevents heat transfer. If one of those panes cracks, the gas escapes, and the window loses its efficiency. 

When you think of a cracked window, you might imagine the stereotypical flying baseball crashing through. Sometimes, though, window glass can crack on its own with wear and tear or fluctuating temperatures. Even curtains can contribute to window failure. “By dropping the curtains down, it doesn’t allow the heat to travel through both panes of glass and traps it. A lot of times, it can crack glass if it gets too hot, or it can break the seal in between the two pieces,” says glass specialist Rich Rosenfeld.

Watch This Old House general contractor Tom Silva work with Rosenfield to repair a homeowner’s cracked window.

Repair Options for Double-Pane Windows

Depending on the type of window damage, you have several different repair options.

Replacing the Sash

“A lot of homeowners think we have to replace the entire unit. Well, in some cases, that’s true. But there are also manufacturers out there that will make you a sash only,” says Silva. “You give them the window dimensions, they make the sash, and you can put it in good as new.”

Sash replacement is a lot more cost-effective than repairing the whole window. It could be your best option if the frame is still in good condition and the manufacturer still makes sashes fit for your roof.

Replacing the Glass Assembly

“There are also companies out there that will make just the glass to fit into the sash that you have,” says Silva, “but you have to take the sash apart to do it.” Glass repair can be less expensive than even sash repair. A professional technician removes the damaged glass, then installs a replacement pane custom-fit for the window’s measurements.

Replacing the Entire Window Unit

Ideally, you’d only have to replace a few components of your window. However, you may also opt to replace the whole thing. It’s usually the most expensive choice, but if there’s damage to the frame, the window is very old, or if replacement parts aren’t available anymore, it may be your best choice.

Tips for Choosing Replacement Materials and Services

When opting for repairs, select the right materials based on longevity and cost-effectiveness. Here are some tips for making the best choices:

• Choose value, not cost: While it might be tempting to opt for cheaper materials, don’t do it for its own sake. Instead, find materials and services that deliver the most value. A high-quality repair may be more expensive, but it will usually last longer and perform better.
• Check for compatibility: Make sure that the replacement parts are compatible with your existing window setup. Incompatible materials could damage the window, or at the very least make it far less efficient. Work with a professional who can help you choose the right fit.
• Get a warranty: Choose materials, parts, and companies that offer a good warranty. This will give you better peace of mind and protect your investment against further defects and issues.

If you’re working with a professional, get quotes from multiple different companies before you make a final decision. Check reviews online, ask for references from your neighbors and friends, and verify that the technicians hold the proper licenses and insurance required by your state and city.

The Glass Replacement Process

After assessing the damaged window in the video, Silva determines only a glass replacement is necessary. The process starts by assessing the damage and taking measurements. Once the replacement pane makes it from the factory to your home, it’s a simple installation process, but demands special care to keep a tight seal.

Measuring the Window

Rosenfield starts by measuring the window for a proper fit. He uses a tape measure to determine the width and height of the new glass and then measures the thickness of the glass with a specialized caliper. “We send all the sizes to the glass manufacturer,” says Rosenfeld. 

The Manufacturing Process

Replacement window glass starts out as large sheets. Machines programmed with the proper dimensions score the glass. A human worker carefully snaps each pane off. “Because this is insulated glass, we need two pieces the exact same size,” Silva says. The workers deep-clean the glass with a heavy-duty scrubbing system.

The factory also makes the metal frames that hold the glass together. A machine twists and folds the metal to the right size, and a worker fastens both ends together with a clip to make a closed rectangle. Next, they drill the frame to install an insulating layer that resists moisture and install sealant along the outside that holds the two panes together.

Finally, a worker attaches the frame to one of the glass panes. A specialized pressing machine injects argon gas between the two panes and seals the assembly shut. A final bead of polysulfide sealant along the frame’s perimeter finishes the job.

Removing the Old Glass

In a week or two, the glass will arrive from the factory and Rosenfeld can start the repair process. He removes the sash from the window, then takes out any stops holding the window to the frame with a pry bar and rubber mallet. Next, he cuts all the way through the sealant with a utility knife and carefully presses the window assembly out of the frame.

Glass is sharp, so it’s best to use rubber cut-resistant gloves for the process.

Installing the New Glass

To install the new glass, Rosenfeld squeezes a thick bead of caulk around the sash’s inner perimeter, where it comes in contact with the glass assembly. He carefully places the assembly into the bead, presses down to tighten it, and reinstalls the window stops and any other hardware.

Let the caulk cure for at least 48 hours before you open or close the window.

Resources

Assistance and materials were provided by Banner Glass Shellmar and Thermal Seal Insulating Glass Inc., Uxbridge, MA.

Silicone caulk can be purchased from The Home Depot.