What if you could keep your house at least 12F degrees cooler than the outside, in the height of summer, without air conditioning, fans, or any other power? How often would you even need A/C at that point? If you have a pair of scissors, an afternoon, and a couple hundred dollars or less to make it happen, read on.

There’s a material out there called shade screen. It’s like window screen, but it’s designed to block more light. Apparently it’s used most often in hot climates as a replacement for standard window screen, to cut down on sunlight. Similar products are used to keep greenhouses cool.

The window screen version doesn’t show up much in cooler, more seasonal climates. I’m not sure why. It could be because while blocking out the sun is good when it’s hot, it’s not really desirable when it gets cold. Lack of sunlight in winter can be depressing enough without any help from your window screens.

But still… commercially available shade screen can prevent 80-90% of the sun’s hot rays from entering your house. With summer temperatures here regularly over 90F, and plenty of humidity, I thought there must be a way to take advantage of this stuff without it being a giant pain, and without losing the winter sunshine.

My first thought was two sets of screens – one for summer, and one for winter. But that didn’t come close to passing the “pain-in-the-butt” test. My next thought was to attach the shade screen to the existing screen frames with velcro. That proved to be somewhat ineffective, as the sticky backing of the velcro heats up and becomes less sticky. The adhesion between the screen and the velcro wasn’t very good anyway.

Finally, I realized that most of our windows slide down from the top as well as up from the bottom. If I put the shade screen between the window and the original screen, and then pin the top of the shade screen by closing the window on it, I’d be all set. No muss, no fuss.

I removed one of our window screens and used the frame as a template to cut the shade screen. I put the original screen back in place, opened the window from the top, slid the shade screen down between the glass and the screen, arranged it to the best fit, and then closed the top part of the window.

It worked like a charm. On a hot July day, with the sun beating down, I compared the surface temperature of the window with the shade screen to another nearby window.

After ten minutes, there was a 21F degree difference!

Lucky for me, all but a few of our windows are the same size. I took a screen back out and used it as a template to cut shade screen for all the other windows. I cut it maybe an inch wider and a few inches longer than the frame. It couldn’t have taken an hour to cut enough for the whole house.

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You may be wondering if it would be easier to just draw the curtains or hang shades in your windows. This shade screen approach has two major advantages: 1. You can still see out, and more importantly 2. The sunlight is blocked before it goes through the glass. Halting the sun’s rays after they’re already inside isn’t nearly as effective.

I’ve found that there are a number of other advantages to this approach, along with a couple minor drawbacks.

Advantages:

• Easy to implement for summer. I’d estimate 30-45 minutes to put them in all the windows in our house.
• Even easier to take down for cooler seasons. It took me less than 15 minutes to pull them all down, roll them up, and put them away.
• If the window is open and there’s any wind at all, the bottom of the shade screen is free to blow in the breeze and let the air flow in.
• If you want the shade screen out of the way – to let a breeze in, or to accomodate house plants – you can just roll it up as far as you need and tuck it behind the window pane.
  
• You get a privacy effect. From the inside, you can see out just fine. From the outside looking in, it just looks black…
• It cost me under $200 for a 100-foot roll of 36-inch screen, and I only used half of it for the whole house – a dozen double-hung windows, plus the sliding door.

Disadvantages:

• If it’s raining and windy and you leave your window open, the shade screen will catch the water, and then fling it around the room as the wind blows the free-hanging bottom part of the screen
• You get a “wavy” appearance because the shade screen is not pulled perfectly flat. (This photo makes it look worse than it is, but you get the idea.)

Of course, my approach won’t work in every house. Your windows may not be the same as mine, so you may have to come up with a different method if you’re going to try this.

I can tell you that getting it to stick directly to glass is challenging. We have a sliding glass door that gets a lot of afternoon sun. I first tried attaching the screen to the glass door with long strips of velcro. It quickly became clear that this wasn’t going to work because of the heat. The adhesive just wasn’t holding up. I tried sewing the velcro strips to the screen, which worked a little better, but the then the velcro adhesive failed on the glass surface – again because of the hot sun. My next attempt was with some suction cups. It worked “sort of,” so I bought more of them to see if there was strength in numbers. I haven’t had the chance to try it yet, but I give it a 50-50 shot. It’s a pretty big piece of shade screen, so it’s got a bit of weight to it – especially when it’s wet and windy. If anybody has suggestions, let me know.

At any rate, with the windows open at dusk, the whole house fan pulling in the cool night air, and the shade screen keeping the sun out during the day, we can consistently keep the house at least 12F degrees cooler than the outside temperatures on a hot summer day. If I can work out a way to keep it on the big west-facing sliding door, we might even get a few more degrees out of it.

For reference, I bought Phifer SunTex 80 from Wholesale Screens and Glass. (They also sell SunTex 90, which blocks even more sun.) I’m sure other vendors and similar products would do just as well.