How to Replace Insulating Glass

Three ways to fix a broken or fogged-up double-pane or Thermopane window.

By Art Rooze and Duane Johnson

From The Family Handyman Originally in How to Replace Insulating Glass

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About this Project

It used to be that a broken window was a $5 fix—a piece of glass, some glazing compound and a few minutes’ work—and then tell the kids to play ball somewhere else next time.

But it’s not always that easy these days. There’s a lot of high-tech, double-pane insulating glass around that not only gets broken but also can lose the seal between the panes and permanently fog up.

Replacing a piece of insulating window glass gets expensive. The glass itself costs anywhere from $30 to $120. And often you have to hire a pro to do the job, which can bring the total to well over $200!

This article shows how you can cut this cost by replacing insulating glass yourself. Sometimes the job is so easy that almost any novice can do it. But other windows can be so difficult that you’re better off turning them over to a pro. We’ll tell you how to figure out whether you can do it yourself.

Repair Strategy
Start by removing, if possible, the entire sash containing the broken or fogged-up insulating glass (see “Removing Window Sashes,” below). Take it to a window repair specialist at a glass shop. Look under “Windows” or “Windows, Repair” in the Yellow Pages, and call first.

The specialist will measure the size and thickness of the glass panel, help you identify the manufacturer and determine if a fogged-up window is still under warranty (see "Warranties"). Some special kinds of glass like low-E and gas-filled units must be special-ordered.

The window specialist will estimate the price of new glass and also tell you the cost to install it in the old frame (usually $30 to $60). Installation costs will double or triple if the specialist has to come to your home. Prices can vary quite a bit, so call around to compare prices of both the glass and the installation.

If you buy the glass and install it yourself following our step-by-step photos, also buy any of the supplies you’ll need from the repair specialist. Ask for advice so you’ll know whether the job’s just too big for you to get into, or not worth the money you’ll save. Keep in mind that glass dealers may not warranty the glass if you install it yourself. Be sure to ask. You should expect a 10- to 20-year warranty against seal failure.

Removing Window Sashes
Most insulating glass sashes are easy to remove if they’re the type that you can open. But you can’t always remove stationary sashes. These have to be repaired in place. Here are the most common types of openable sashes and how to remove them.

Double-hung windows slide up and down. Those with insulated glass almost always slide against vinyl jamb liners on the sides. To remove the sash, depress the liners slightly, then pull out the top part of the sash. Twist the sash to release one side from the counterweighted springs that connect to the sash bottom. To reinstall it, put the bottom in first and reverse the procedure.
Casement windows are hinged on one side and swing outward when you turn a crank. The swing arms that hold them usually have release catches. But if you can’t figure out the release mechanisms, simply unscrew the arms at the top and bottom to release the sash. Have a helper support the window while you unscrew it.
Slider windows move horizontally. You can usually remove them just by lifting the sash and swinging out the bottom. If nails holding the trim in place prevent you from lifting the sash, cut the nails with a side-cutting pliers or a hacksaw blade, or pull them out.

Here’s How to Do It
Manufacturers install glass in window frames in three different ways: with gaskets, adhesive tape or caulk. We’ll show each method, starting with the easiest.

Gasket Method
FIG. A GASKET

In this installation method, the edges of the insulating glass are wrapped in a one-piece molded gasket of vinyl or neoprene. The frame is held together by four screws, one at each corner. The grooves in the frame hold the window in place. Sashes assembled by this method usually come apart easily, and they are just as easy to reassemble.

Some Additional Tips:

Our photos show dismantling a wood sash, but sashes may also be vinyl or aluminum, and they usually come apart the same way.
Be careful not to damage the old gasket, so you can reuse it. Replacement gaskets can be hard to find.
Always use “neutral cure” silicone for caulking. Common brands include Silicone II (GE), Trade-Mate II Paintable Silicone (Dow Corning) and Silicone XL II (M-D).