Things You'll Need
Existing single pane window
4.5mm plastic edging
Protective rubber gloves
Butyl mastic adhesive cartridge
3mm glass pane already cut to size
Window glazing cartridge
Windows with single panes can be drafty and increase your heating and cooling costs. Double pane windows are far more efficient, but they can cost a lot of money. Sometimes double pane windows are so expensive that it simply doesn't make financial sense to upgrade. However, you can construct your own double pane windows with some time and a few basic supplies.
Place the single pane window on a firm surface in front of you, interior side up. Without damaging the original window, remove the glazing from the window pane by scraping it off with the putty knife. Clean the glass with glass cleaner and wipe clean with a soft cloth. Allow the window to air dry.
Examine the plastic edging that holds the pane in place. It should rise above the pane slightly. Trim the edging so that it is flush with the window pane.
Cut two strips of plastic edging the same width as the window. These will be placed at the top and bottom of the window, so measure carefully.
Put on the rubber gloves and apply a strip of butyl mastic adhesive directly to the window pane along the top and bottom. This adhesive should cover the edging of the window and a small amount of the window pane itself.
Press the strips of edging firmly into place, one at the top of the window, the other at the bottom. You have to apply some pressure to ensure that the adhesive bonds to the edging. The U-channel of the edging should face toward the center of the window pane. When finished, wipe away the excess adhesive with an old rag.
Cut two strips of edging to fit on either side of the window pane. Secure them into place in the same manner as the top and bottom strips. Allow the adhesive to dry according to the manufacturer's directions.
Apply a small amount of adhesive to each corner to seal the gaps between the edging. If you measured correctly, the gap should be relatively small, but it still needs to be sealed. Also apply a small amount of adhesive behind the edging to secure it to the window pane. You may have to pull the edging away from the pane slightly to get the adhesive in place. Press the edging back into place and allow the adhesive to dry according to the manufacturer's directions.
Clean the new pane of glass with the glass cleaner and wipe with a soft cloth. Allow the glass to air dry. When the glass is dry, run a small amount of adhesive around the edging and press the glass into place. Apply light pressure so that the adhesive bonds to the glass and the edging.
Install the glazier's points around the edge of the glass, approximately 4 inches apart, according to the manufacturer's instructions. Set a new double pane window aside and allow the adhesive to dry and cure thoroughly. This may take up to 36 hours, but consult the manufacturer's directions on the adhesive you're using to know for sure.
Apply a small amount of window glazing to the outer edge of the new pane of glass. Spread the glazing around the glass with a clean rag, covering all exposed glass equally. Allow the glazing to dry according to the manufacturer's directions. When the glazing is dry, the window can be painted or installed.
Most hardware stores will cut a pane of glass to any size you need.
Handle the glass gently to avoid breaking either the new pane or the existing window.