How to Insulate Windows from the Summer Sun (Cheaply!)

I live where it gets hot in the summer!

One of the upstairs rooms has 3 enormous west facing windows so the hot afternoon sun bakes this room for several hours each day.

Even though the windows are double paned, the windows, the shades, and the room really heat up by early evening.

We have a swamp cooler, and a ceiling fan in this room, but it’s an uphill battle against that hot sun.

We brain stormed how best to insulate the windows cheaply and came up with several ideas.

We first considered putting cardboard panels in the windows. Because the windows are each 3 feet by 5 feet, we would need a very large refrigerator box to make cardboard panels. I tried for several days to get a refrigerator box, with no luck.

We had already bought a dozen sheets of foam board (poster board that kids use for school projects – they have a thin foam core between paper sheets) at Dollar Tree to attach to the cardboard for extra sturdiness and insulating qualities as well.

Since the cardboard wasn’t available, I decided to proceed with just the poster board.

It took 4 poster boards for each window because they are so large.

Materials.

Foam Poster Boards from the Dollar Store

White Duck Tape (Use the real thing – the Dollar Store duct tape doesn’t stick as well.)

Yardstick

Scissors

Craft Knife

Measure the windows carefully – twice! I almost goofed and made the wrong size.

Figure out the best way to lay out the poster boards to fit the window with a minimum of waste.

I could not cover the window with less than 4 poster boards, which were 20×30. So each window only cost $4 for poster board, and then some duct tape – probably 1/2 roll (for all 3 windows) which costs less than $3.50 a roll at Walmart.

Measure and mark the poster boards to fit your window. I had to cut down the sides of 2 poster boards, and cut a little off the top of 2 of them.

To cut the poster board, I laid it on the coffee table with the smaller area to be cut off hanging over the edge.

I sharpened my craft knife, laid a metal ruler along the marked line, and cut right up against the ruler for the length of the poster board. (If you use this method, make sure your knife will be cutting slightly away from the edge of your coffee table so you don’t damage the table.)

Lay your cut pieces of poster board out on the floor in the configuration needed to fill the window. Push all the inner edges up against each other.

I used boxes and other straight edge items against the sides, top, and bottom to help align the pieces and hold them in place.

Starting at the center joint, I adhered duct tape all the way across. Leave a few inches overhang on each side to fold under and adhere to the bottom, to help hold the boards together.

Gently but firmly, press the duct tape down to be sure it adheres to the poster board.

If you have a brayer, you can use it gently to help adhere the tape to the foam boards. Or use a hard edge, such as a ruler to gently adhere the tape.

To do the lengthwise joints, I started a few inches above the center, then taped all the way down. I left a few inches extra to tuck under the bottom and adhere to the other side.

I gently lifted up the finished piece and slid it under the shade already on the window. Because the foam board is so thin, it fit right under the shade, which will hold it in place.

Almost the instant I put the foam board in place it felt cooler standing next to that window.

I used the piece I cut off my first board as a pattern for how to cut the rest of the pieces. Just lay it along one edge of the board and mark it. If you’re doing more than one window, be sure to use the same pattern piece, or the piece you are cutting off will be getting bigger and bigger, and make your finished piece too small for the rest of the windows.

I lightly wrote “Pattern” on the first piece I cut, that I was using for a pattern.

When I went outside to see how the newly insulated window looked, I could barely find the joint, and then only because I knew it was there and where to look for it.

The window with the insulation looks exactly the same as the other 2 that just have shades.

I left the poster boards in the windows over the winter, too, and they worked well to keep the cold out and the room warmer.

© Noreen Doll