How to Install Plastic Windows

Installing plastic windows is perhaps one of the more basic window replacement projects you can tackle. With some basic DIY experience and a short list of supplies, you can add plastic windows to any room in your home. Here's how.

1. Prepping for Plastic Windows

Remove the old sash by disengaging the two sets of removable stops--the one that holds the lower sash in place and the stop that separates the sashes. Pry these off carefully because you'll be able to reuse them.

2. Setting the Plastic Windows

Set the replacement plastic windows in the opening. They will fit snugly between the stool on the inside and the outside stops. If the new plastic windows are narrower, you may need to shim the gap between the plastic windows and the outside stop.

3. Supporting Plastic Windows

Set the edge of a board at an angle that roughly matches the slope of the sill and then cut a strip of wood to match the gap. Cut the support strip to length and nail it directly beneath the point where the front edge of the new plastic windows will rest.

4. Centering the Plastic Windows

Center the plastic windows in the opening using a carpenter's square to make sure the plastic windows are square. Shim the sides of the plastic windows directly behind the screw holes in the jamb. Screw the plastic windows in place through the side jambs, then replace the inside stop.

5. Finishing Touches

Check the plastic windows from the inside to make sure they operate smoothly. Then insert a narrow bead of caulking all around the plastic windows to seal the gap at the outside stop.