How to Upgrade Glass on Existing Wood Windows

Upgrading the glass in your wooden window frames can increase your home's energy efficiency.

Upgrading the glass in your old wooden windows can greatly increase the overall energy efficiency of your home by saving you money on heating and cooling costs. Modern window glass is available with a microscopic coating that helps to insulate the glass and keeps energy from transferring through the window. This "Low-e glass" is available in a variety of different insulated values. Replacing your old window glass with Low-e glass involves removing the old glass, cleaning the frame and installing new glass in place.

Things You'll Need

• Gloves
• Eye protection
• Utility knife
• Putty knife
• Pry bar
• Flat-head screwdriver
• Claw hammer
• Cordless drill
• Assorted bits
• 120-grit sandpaper
• Primer
• Paintbrush
• Window glass
• Glass cutting tool
• Tape measure
• Glazing putty
• Exterior paint
• Silicone caulking
• Caulking gun
• Finish nails
• Weather stripping

Instructions

Remove the Window from the Window Opening

1. Pry away the exterior trim from around the window. Use a pry bar to lift the exterior window trim. If necessary, cut away any caulking or sealant with a utility knife. Be careful as you take off the window trim; you will want to reinstall it after you've replaced the window.

2. Cut away caulking or sealant from around the window frame with a utility or putty knife.

3. Find and remove the fasteners holding the window in the window opening. These may be either screws or nails. Back screws out with a cordless drill. Use a flat-head screwdriver to raise nail heads and use a claw hammer or the clawed end of a pry bar to lift and pull the nails holding the window free.

4. Pull the window free of the window opening and set it on a flat workbench or work area. Lay down a drop cloth under your work area to collect any glass shards or pieces that may result from a broken window pane.

Remove the Old Glass and Clean the Window Frame

1. Cut away the caulking or glazing holding the original glass in place. Wear gloves whenever working with windows and glass to avoid injury resulting from broken glass shards. You may have to break the old glass panes and remove the individual shards. Remove all of the glass from the wooden window frame.

2. Scrape away any residual window glazing with a paint scraper.

3. Sand the window fame to remove any loose paint. Sand the wooden window frame with a piece of 120-grit sandpaper.

4. Wipe the frame with a clean cloth to remove dust created during the sanding process.

5. Prime the wooden window frame with a quality exterior primer. Apply the primer with a paintbrush. Let the primer dry completely before affixing the new window glass to the window frame.

Glaze the Window

1. Measure and cut your window glass to fit into the window frame. Make the finished piece of glass 1/8-inch shorter than the length and width of the inside of the window frame into which the glass will be fit. The glazing material will fill the small gap left between each edge of the cut glass and the edges of the window frame. Use a glass cutter to score the glass; then snap off the excess glass along your scored line. Wear gloves and eye protection when working with glass.

2. Apply a 1/8-inch-thick bead of window glazing putty to the inside of the window frame, where the glass pane will rest.

3. Press your glass pane down onto the bead of window putty. Then position "push points" every six to eight inches along the edge of the glass. Press the push points down into the window putty so that they will hold the window glass into place.

4. Lay a thicker, ¼-inch bead of putty along the edges of the window glass. Use a putty knife to bevel the putty and spread it from the face of the glass to the face of the wooden window frame.

5. Use a utility knife to cut a smooth, straight line along the edge of the putty bead, where it meets the window glass. Make one long, smooth stroke with your knife. Use your putty knife to scrape away any excess glazing material left on the face of the window glass.

6. Let the glazing putty dry for at least 48 hours. Then paint the window frame and glazing putty with an exterior paint in the color of your choice. Make sure to paint the glazing putty, too, as this will keep it protected from the elements and elongate its lifespan.

7. Attach weather stripping to the back side of the window, meaning the side of the window that will be pressed against the window opening. Run peel-and-stick weather stripping along the edges of the window to create a weather-resistant seal around the window after it is fitted into the window opening.

Reinstall the Newly Glazed Window

1. Apply a generous bead of silicone caulking around the window opening into which the window will be installed.

2. Press the window into the window opening. Drive a 2-inch screw through the upper side window jamb and into the wood of the window opening to hold the window in place.

3. Check the window for level and plumb by using a level. Make adjustments to the window level by inserting thin wooden shims between the base of the window opening and the window frame.

4. Fill narrow gaps, measuring ¼ inch or less, between the window and the window opening with caulking. Fill larger gaps with foam rubber backer rod cut to size with your utility knife. Then caulk the seams around the window.

5. Replace the window trim. Run a bead of caulk around the inside and outside edges of the window trim.

Tips & Warnings

• Always wear eye protection and gloves when working with glass.

References

• This Old House: Repairing Wood Windows
• James Dulley: Select the best replacement windows (style, frame, glass) for your home
• This Old House: How to Install Replacement Windows

Resources

• This Old House