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How do I Build Polycarbonate Storm Windows?

Updated July 19, 2017

Polycarbonate is one of the strongest plastics produced, having 250 times the impact resistance of glass. Storm windows are designed to protect a house's interior, adding an extra layer of protection against foul weather. Storm windows keep cold air out and heat in during the winter, saving money on heating bills. Having a professional window company install storm windows can be expensive. Use a few basic tools to build and install simple storm windows, saving the cost of having a professional do the work.

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  1. Measure the length and width of the windows being covered. Measure each individual window because there can be small differences. Label each window (window 1, window 2 and so on) using a piece of painter's masking tape adhered to the glass.

  2. Write down the measurements of each window. Add an extra 2 inches to the length and width to account for the window frame. This leaves a 1-inch border around the window. The storm windows will be mounted directly to the window frame with screws. The extra length and width allow holes to be drilled through the 1-inch border and into the window frame. Use ¼-inch thick polycarbonate, which can be cut to specific measurements by a plastic retailer.

  3. Mark the positions of the screw holes needed to mount the polycarbonate storm window. A general rule of thumb is one hole every 12 to 16 inches. The holes should be ½ inch from the outer edge of the polycarbonate sheet. Leave the protective paper or plastic backing on the polycarbonate sheet, using a grease pencil to mark the positions of the holes.

  4. Drill the holes into the polycarbonate sheet, using a drill bit that is a slightly larger than the screw's diameter. The screw should fit loosely into the hole. Sheet plastic can expand and contract with changes in temperature. If the screw hole is too tight, the polycarbonate sheet will buckle around the screw.

  5. Sand the edges of each polycarbonate sheet by hand. This reduces any sharp edges that could cut fingers when installing or removing the storm windows. Use 120-grit sandpaper, which will remove the sharp edges quickly and leave a smooth edge on the sheets.

  6. Mount the storm window. Use painter's masking tape to lay down guide lines for placing the polycarbonate sheets on the window frame. Position the polycarbonate sheet on the window frame, marking the positions of the holes on the window frame with a grease pencil. Drill pilot holes and screw the panel in place. Use rubber washers placed between the screw head and the polycarbonate panel to reduce expansion and contraction problems.

  7. Tip

    Buying and cuttine full, 4-by-8 sheets of polycarbonate is less expensive than having a plastics retailer cut the sheets to size. Polycarbonate can be cut using a table saw with a 60 tooth blade. Unlike acrylic, polycarbonate can be cut with conventional woodworking tools rather than specialised equipment. A bead of caulking can be used to seal window frames that are bowed or uneven.


    Always leave at least one window accessible as a fire escape. The storm window on this exit window can be held on with exterior double-sided mounting tape, which will allow it to be kicked out in the event of an emergency. Never seal all the windows in a room.

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Things You'll Need

  • Sheet polycarbonate
  • Screws
  • Rubber washers
  • Drill
  • Drill bits
  • 120-grit sandpaper
  • Painter's masking tape
  • Grease pencil

About the Author

Hugh Patterson

Hugh Patterson started writing poetry in 1978. He started writing fiction and non fiction in 2003. His work has appeared in "The Nervous Breakdown" magazine and a number of other literary journals. He also writes online book reviews. He studied chemistry and design at Ventura College and had a California Math and Science Teacher's Fellowship through the University of California Santa Barbara.

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