Storm windows are an important part of insulating your home against adverse weather and heat or cold. By creating a sealed air pocket between the inner and storm window, you can dramatically increase the insulating capacity of your windows. However, for older houses with wooden framed windows and no storm windows, having storm windows professionally retrofitted can be very expensive. Luckily, there is a fairly cheap and uncomplicated way to create your own storm windows from Plexiglas.
Measure your window frame(s). You will want your storm window, including its wooden frame, to be about 1/8-inch smaller on all sides so that it can be held in place by the foam weatherstripping.
Cut four pieces of one-by-two lumber to fit the four sides of your window, less 1/8-inch.
Miter the ends of the lumber with a 45-degree miter cut on your saw.
Rout a line 1/4 inch deep and as thick as your type of Plexiglas on the inside edge of each piece of wood.
Cut your Plexiglas sheet to fit inside the wood frame, adding 1/4 inch on all sides so that the sheet fits perfectly in the routed groove of the frame. Cut the Plexiglas by scoring it deeply on both sides with a utility knife. Then place the scored line directly along the edge of a table, and break the Plexiglas along the line by pushing down firmly.
Insert the cut Plexiglas into the routed grooves in the frame. After the frame is assembled around the Plexiglas, staple the corner joints.
Apply silicone caulk along the inside edges of the frame on both sides of the window and allow to dry according to the caulk manufacturer's specifications.
Place lines of adhesive-backed foam weatherstripping inside the window frame, and then push the Plexiglas storm window into place. The foam will hold it up firmly, and you can remove it when the weather changes or when you wish to open the window.