How to Make Old Windows More Energy-Efficient
Learn how to complete a variety of window maintenance projects, including installing double-glazed units and removing broken glass.
Window maintenance is an often overlooked part of home improvement. Replacing older windows with energy efficient windows is a popular DIY project. But not all older windows need to be replaced when you encounter problems, and some historic districts have very strict guidelines. Some windows may need glass replaced, paint removed, caulk to seal the air leaks or ropes replaced. Older windows are hung on ropes and need to be properly balanced to open and close properly. If you have older windows, you may want to invest time and money in restoring them. Newer windows may be more difficult to update and repair, as they often available only as units.
Clean the rabbet before you start. Cut some putty from its container with a putty knife. If it is particularly sticky, spread a small amount of powder filler on your hands, and coat the putty itself with more filler to make it easier to handle. Work it in the palms of your hands so that you achieve a malleable, smooth consistency before you begin.
Work from the outside. Roll the putty into strips about 3/8 inch in diameter. Press the strips into the rabbet (Image 1).
Maneuver the glass into the rabbet. Press gently around the edges of the pane (Image 2).
Hammer glazing pins into the rabbet, not quite touching the glass. Their heads will be hidden by the finished putty. Use cardboard to protect the glass (Image 3).
Press more strips of putty into the junction created by the glass and the rabbet using your thumb (Image 4).
Use a putty knife to trim excess putty from behind the glass, then draw the knife along the external putty to create a smooth seal. Miter the corners neatly (Image 5).
Remove smears from the glass with mineral spirit. Before painting, let the putty dry until a hard skin has formed on its surface (Image 6).
Replacing Wooden Beads
Wooden glazing beads are attached to the exterior of the frame to secure panes of glass. They can be used to glaze a window that was previously puttied. A snug fit is essential to ensure that the glass is secure and weatherproof. Glazing silicone is used to seal the joint.
Apply window caulk around the rabbet to one-third of its depth. Press the pane gently into position to create a seal (Image 1).
Nail each bead in place on the silicone, using at least two glazing pins for each bead. The inner edge of each bead should sit flush against the glass. Wipe off any excess silicone (Image 2).
Installing Double-Glazed Units
Double-glazed windows have two layers of glass separated by air space, which creates nearly twice the insulation as single glazed units. Glass does not provide insulation value. It is the air between the layers of glass that creates the insulation of an air pocket. Some types of double-glazed windows also use a plastic film as an inner glazing layer. While you can achieve a similar result with a storm window, it is not as effective as there is heat loss along the frame of the storm window.
If you add a third or fourth layer of glass, the insulation value of your window will increase. Each layer of glass traps some of the heat that passes through, increasing the window’s resistance to heat loss. When double glazing windows are manufactured, the air between the glass is dried and then the space is sealed airtight. This eliminates possible condensation problems later. Some double-glazed windows are made with a reflective coating, which helps the insulation value.
Place two packers along the bottom of the glazing rabbet. Vinyl glazing systems vary, so follow guidelines specific to your system. Further packers may be required around the edge of the unit to ensure that it is positioned centrally and securely within the frame (Image 1).
Position the unit on the packers and push it into the rabbet. Take care not to crease the waterproof seal or gasket as you push (Image 2).
Clip the glazing beads and gaskets into position to hold the unit securely (Image 3).
Replacing a Broken Sash or Cord
Work from the interior. Use a chisel to pry away the beading holding the inner sash in the frame. Cut any unbroken cords attached to the sash so that you can lift it out. Remove the central staff beads and repeat the process to remove the outer sash. Undo the knots or remove the nails holding the old cords to the sashes. With the sashes removed, you should be able to pry the four weight covers out of the frame to expose the weights.
Threading in the Replacement Cords
The easiest way to thread the new sash cord over the pulley mechanism is to use a piece of string with a small weight tied to one end — a small screw or nail is fine. Tie a length of sash cord to the other end of the string. Then, push the nail over the pulley, so it drops down next to the weight. Use the string to pull the new cord over the pulley, being careful not to pull the whole length over. Tie the cord to the weight — you may need to remove the weight from the frame to do this. Repeat for the other three cords.
Replacing the Sashes
Hold the outer sash up to the frame in the fully open position. If your sash cords are knotted in place, pull the cord taut, and mark the cord where it reaches the hole. Lower the sash, then thread the cord through the retaining hole, and knot it at the marked point. If your cords are attached with nails, the technique is similar but you should mark the position of the top of the sash on the taut cord. Lower the sash, realign your mark, then nail the cords in place along the sash edge. Check that the sliding mechanism still fits. Fasten the staff beads in position and refit the inner sash. Finally, replace the weight covers and beading.
Removing Broken Glass
Wear thick gloves, work boots and goggles when working with glass. Put masking tape over the glass to prevent falling shards, then remove the putty or beading and tap out the pane in one piece. If this is not possible, break the glass and dispose of it carefully. Clean the rabbet before you reglaze.
Glass is traditionally held in place by putty or glazing beads. However, aluminum and vinyl windows often use gaskets and cover strips to form a watertight seal. If you purchase windows with a special system, use it as instructed.
It is unlikely that you will be able to replace a broken pane immediately, so do one of the following in the meantime:
• Patch small cracks with clear glazing tape.
• Stick masking tape across badly cracked glass, then stretch polythene sheeting over the window, using furring strips to stop it from tearing. This will keep the weather out until you can reglaze.
• If security is an issue, cut a sheet of plywood or hardboard to size and screw it to the frame.
Install a Mortise Casement Fastener
Most side-opening casements require one fastener, although larger ones may need two, as will large awning windows. Installing fasteners is a straightforward procedure that simply requires accuracy in positioning. For hook or wedge fasteners follow the first three steps below, then pilot and screw the hook or wedge in position on the window frame.
Remove the old fastener. Fill the holes with wood filler. Sand the filler smooth when it is dry. You can buy colored fillers that are almost invisible in wood with a natural finish. If your window is painted, you will need to prime over the filler before touching up the paint (Image 1).
Hold the fastener in position and mark the screw holes (Image 2).
Drill pilot holes in the casement frame at the points you have marked. Screw on the fastener (Image 3).
Close the casement. Swing the fastener toward the window frame. Position the mortise-plate so the arm touches the frame in the middle of the opening. When you are happy with the position, use a pencil to draw around the edge of the mortise-plate and its central opening. This will provide a guide for chiseling out the mortise (Image 4).
Chisel out the mortise and a rabbet for the plate. The mortise depth should be slightly greater than the length of the arm (Image 5).
Mark and drill pilot holes at the attachment positions. Reposition the mortise-plate and screw it in place (Image 6).
View photo gallery instructions for this project