How to Replace Window Glass

Before you replace broken window glass with a new piece, measure the height, width and opening of your pane, and the thickness of the old glass. Write these measurements down. Most home improvement stores will cut glass to order. If you prefer, you can order a large glass sheet and cut it to the correct size.

Order your new glass pane (or cut it yourself) at least 1/16 inches shorter in all directions. Always test fit the glass dry before setting it in place. Along with the glass, purchase a new package of glass points. These are the small metal triangles that secure the glass into the putty. If you have vinyl or aluminum windows, these will require double-sided foam tape or silicone.

Many modern residential windows use insulated glass units (IGU) rather than single panes. IGUs are made of two panes of tempered glass that are separated by a spacer. The space between the two panes is filled with a gas.

IGUs generally have to be ordered from a glass manufacturer, and they come in assorted sizes. When trying to replace window glass in modern windows, it helps to be familiar with taking proper measurements for an insulated glass unit. There are several things to note to make sure that you get the best fit and the right glass.

• Measure the height and width of the unit.
• Measure the thickness of the glass sheet.
• Measure the thickness of the overall unit.
• Note the spacer color – usually white, black or metal.
• Note the coating of the old glass – this is usually low-E, but it might also have a tint.

You also need to note the type of glass. You can generally tell this by the way in which the old glass broke. If the glass broke in large, jagged pieces, it is likely annealed glass, which is the most common.  If the glass crumbled into tiny pieces, it is most likely safety glass.

Take the specific measurements of the broken unit and then call for a replacement. As with an ordinary glass pane, tape heavily over any broken or cracked areas in the IGU before beginning the repair. When learning how to fix a broken window, taping the glass will always be important for safety.

Once you’ve removed broken glass, you need to prep the frame to be re-glazed. 

• For a wood frame window, use a wire brush and clean out any dirt and residue on and inside the window frame.
• With traditional glazing, soften the old compound with a heat gun, being careful not to scorch the wood.
• Scrape away the softened material with a putty knife.
• Remove the metal glazing points from grooves in the frame where the glass was held.
• Scrape away any remaining old paint or compound in the l-shaped grooves. Then, sand the grooves down to bare wood.
• Coat the bare wood with a sealer and let dry. For older wood windows, use a small brush and apply a few coats of linseed oil instead to the wood around the frame. Let the oil soak in. This will extend the life of the glazing.

• Use a caulking gun and squeeze a thin layer of window glazing compound in the primed grooves.
• With the help of a friend, set the new window glass in place.
• Press the new window glass lightly to bed it.
• Press in new glazing points every 10 inches with the tip of a putty knife.
• Apply additional glazing compound by moving the tube tip along the edge of the glass while steadily squeezing the trigger.
• Smooth the glazing with a wet finger or cloth.

Tip: If the compound is applied too thick, you will notice swelling and it will be visible around the pane. 

Take a look at your window frame to make sure it doesn't need a paint touch-up. If it does, follow these simple steps: 

• Lightly scrape away or gently sand any areas of peeling paint.
• Latex glazing can usually be painted the same day.
• Place painter’s tape over the glass in areas that need paint to within 1/16-inch of the glazing. Overlap the paint to improve its weather seal.

When replacing window glass, it is usually easier to remove the window and lay it flat. However, most aluminum windows can be repaired in place without removing the sash. 

• Put on cut-proof gloves and eye protection.
• Pop out the vinyl strip from the aluminum window frame. Insert a flat-head screwdriver or the edge of a putty knife under the strip to start.
• Remove the strip the rest of the way by hand. If the strips overlap, you may have to remove each strip in order, usually side strips first, then top, then bottom.
• Inspect the vinyl strips. If they seem old, worn or brittle, you can purchase new vinyl strips and cut to the correct size with a utility knife.
• Cut away old silicone from the exposed glass. Remove additional broken glass and clean out the frame channels. Scrape away old silicone with a utility knife. Wipe the channels clean with glass cleaner.
• Measure the frame space from top to bottom and side to side to get the correct measurement of the new glass. Subtract 1/16 inches from each side and use these measurements to have the glass cut to the correct size. Dry fit the glass into the frame before sealing it in.
• Run a line of silicone caulk along the back edge of the aluminum frame. Press the glass in place. Hold for a minute to allow the silicone to set.
• Run a line of silicone around the edges of the glass.
• Fit the vinyl strips back into place. Start with the bottom, the top, then left and right strips.

Replacing window glass in vinyl windows is completed more easily when you remove the sash and lay it flat. While the technique is similar to learning how to replace a window pane for an aluminum frame, the glass required often must be bought from a glass manufacturer. 

• Wear eye protection and cut-proof gloves.
• Remove the window sash, according to manufacturer directions. Usually, this is simply pushing in the side latches to tilt the window out, then sliding the window out of its track.
• Remove the vinyl glazing strips from the vinyl frame. Use the flat edge of a screwdriver or a putty knife to gently slide under the edge of the strip and pop it out of the frame.
• Cut away the old foam tape or sealer securing the glass unit. Run the tip of a putty knife around the edge of the inner sash frame to loosen it.
• Once the glass unit is free, carefully lift it out of the vinyl frame.
• Gently scrape the old mounting tape or sealer away from the inner channels of the sash. Try to get the surfaces as clean as possible to create the best seal on the new installation.
• Apply new double-sided mounting tape along each edge. When you reach a corner, cut the tape, then start down the new side, overlapping the other edge at the corner.
• Replace the small rubber pieces, called setting blocks, and the bottom corners of the sash, if needed.
• Peel the backing from the tape to expose the adhesive, then, carefully set the new IGU into the frame. Apply a little pressure around each edge to help it settle securely into the adhesive.
• Replace the vinyl strips back around the edges of the sash frame, pushing them into place by hand.
• Then, replace the window sash and lock it back into place.