How to Replace Insulating Glass

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

Don’t put up with foggy or cracked double pane windows. You can replace them yourself and save the major cost of professional repair. We show you three ways to take the sash apart so you can install the replacement glass.

By the DIY experts of The Family Handyman Magazine

TIME

One day

COMPLEXITY

Moderate

COST

$20 - $100

Repair strategy and buying materials

It used to be that a broken window was a cheap 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. And often you have to hire a pro to do the job, which can get very expensive.

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”). 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 “Window 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. 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.

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.

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.

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Method 1: Gasket seal

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 (Photo 4).

Figure A: Window with gasket seal

Fig. A Window section Gasket seal on window
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Method 2: Adhesive tape seal

Some windows are sealed with double-face adhesive “setting” tape. Usually these windows have removable vinyl, aluminum or wood stops on one side, with the adhesive tape placed between the glass and the frame on the other. The tape is usually 1/16 in. or 1/8 in. thick, so you’ll have enough room to slip a thin-blade putty knife or utility knife between the glass and frame to slice through the tape.

Some additional tips:

  • Pry out the stops, being careful not to bend or break one. Replacements can be hard to find.
  • Some stops can’t be removed without ruining them. Ask the repair specialist if your windows are this type, and buy new stops.
  • Buy double-face glass sealing tape of the correct thickness and width from the repair specialist.
  • If the stops are caulked in place, slice through the caulk with a utility knife.
  • If the window has “setting blocks” (to keep the glass centered in the frame, as in Photo 4), reposition them exactly as you found them around the old glass. But check the fit of the glass first. You may have to alter the thickness of the blocks.

Figure B: Window with a setting tape seal

This is a cross-section of an insulated-glass window.

Fig B window section Setting tape seal
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Method 3: Caulk seal

Insulating glass that’s caulked in place is virtually glued to the frame. In addition, it’s held by a stop, which might also be caulked and very difficult to cut through with a knife. You might have to smash out the window, then pry out the glass piece by piece (Photos 3 and 4).

Tip: For easy cleanup, place glass on top of a sturdy tarp to catch all the shards. Many wood frames have the glass caulked in place, and it’s difficult to replace the glass without damaging the frame. So you might want to consider having a window repair specialist handle this glazing method. If you do it yourself, allow at least a couple of hours to remove the old glass and clean the frame. Some additional tips:

  • Wood stops are usually stapled and painted in place. There’s a pretty good chance you’ll crack them when prying them off (Photo 1). Pros break them too. Work carefully, save the pieces and glue them together later. Finding matching replacement stops can be tough.
  • The wood frames themselves sometimes crack when you pry out the glass. A heat gun, set on low, will soften the adhesive to get the glass out easier, and you’re less likely to damage the wood.
  • Careful; don’t nick the glass when you nail the stops back in.

Figure C: Window with caulk seal

This shows the anatomy of an insulated-glass window with caulk.

Fig C window section Caulk seal
Glass warranties

Most insulating glass now carries a 20-year warranty against defects and seal failure. Older windows may carry a 5- or 10-year warranty. Seal failure is the most common problem. You know the seal has failed when moisture begins to appear between the two panels of glass.

Tip:: Check your warranty at the first sign of fogging.

The fogging might not be all that irritating at first, but in a few years it will be, and by then your warranty may have expired. If you don’t know the window manufacturer, a repair specialist can help you identify the unit.

Major manufacturers usually put tiny identifying marks on the window hardware, the glass spacer or the glass itself. Sometimes these marks include the date the unit was made.

KEEP IN MIND: Warranties cover the new insulating glass unit but not the cost of installation.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Hammer
  • Caulk gun
  • 4-in-1 screwdriver
  • Drill/driver, cordless
  • Dust mask
  • Pry bar
  • Putty knife
  • Utility knife

Gloves, Goggles, Heat gun

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • New insulating glass unit
  • Silicone, neutral cure
  • Glass setting tape