Winterizing Project #3 - Window Sill Insulator

Window sills, especially wider ones, can be cool even if the window is well sealed. The reason this happens is because the window pane itself is always colder than the frame or wall. Cold air is heavier than warm air so falls to the window sill where it pools. If the window frame happens to be metal, the sill can be even cooler. On narrow window sills this effect is counteracted by using window treatments however on some windows, heavy window treatment is not desirable during the day, usually because of a great view. These include bay windows, picture windows and larger sliding windows.

Our walls are about 18 - inches thick on the lower level so we have deep window sills. We would prefer leaving those widows with the water view uncovered. We've all seen it where the homemaker tries to compensate this cooling effect by rolling up a towel or sheet and placing it along the window sill. While this can be low cost and effective, aesthetically it isn't very appealing. I came up with a simple window sill insulator that is inexpensive, easy to make and looks nicer than a rolled up towel. With care, it can be used for several years. The fabric covering is optional but I think it will protect the insulator and it can easily be changed to suit your decor.

Before (1) & With Foam (2)

Measure the area you want to insulate (1). Transfer the measurements to the sheet of foam. Draw the lines in using the Sharpie marker. Using the utility knife carefully cut outside the line. This way you will be able to make small adjustments as necessary. Fine cut along the edges until the foam fits snugly into the spot (2).

Attaching Fabric

Remove the foam and lay good side up on the wrong side of the fabric you are using . Working on the wrong side of the fabric cut around the foam leaving 3-inches on each side (3). Along each edge of the foam, fold the fabric up and secure at intervals using push pins. The corners need to have a square cut out then one side of the corner folded and hot clued before gluing the other portion of the corner (4). This eliminates too much bulk on the corners. Once the corners are secured, hot glue each short end. Then glue one long end, working from one push pin to the next and removing each push pin as the fabric is secured. Repeat along the other long end but pull the fabric slightly and secure by hot gluing (5). If you wish, you can cut another piece of fabric to fit just the bottom then secure by hot gluing but this is not really necessary. Now turn the insulator over and pop into place.

Finished Insulator

The finished insulator in place looks quite nice. I like that it can be popped in and out when needed and can be customized with other fabrics. Slight wrinkles may occur at inner corners if you have them. It will take a day or two for these wrinkles to flatten or they can be carefully flattened using a medium warm iron. If using this method you may have to weigh the insulator down for a few minutes after ironing.

DIY level: beginner level skills

Total Cost: approximately $10

Materials

1 half sheet Styrospan R 5 foam board
piece of firm material of your choice
Sharpie marker
measuring tape
utility knife
straight edge
scissors
push pins
hot glue gun
multi-temperature glue sticks

Garden Gnome
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