James Dulley, a nationally syndicated newspaper columnist, recently wrote about awnings as “cool energy savers.” The sun shining in through windows and glass in doors can quickly overheat a room, Dulley writes. This is the same basic greenhouse effect that is warming the Earth. The sun’s short-wave-length heat energy easily passes through glass into your house. Once in there, it becomes long-wave-length energy. Glass is relatively opaque to this, so it stays trapped indoors. Closing curtains and drapes can help trap the sun’s heat near the window, but it already got indoors through the glass. In contrast, awnings block the sun’s direct rays before the rays enter your house so the awnings are more effective for reducing air-conditioning costs. Studies have shown awnings can reduce cooling needs by 24 percent in Boston, 21 percent in Phoenix, and 17 percent in St. Louis.
From an energy-saving standpoint, the size of the awning is more important than the material. It should shade your window or door from the direct sun’s rays, usually mid-afternoon when it is hottest. Even though the sun is most intense and direct around noon, since it is very high in the sky at that time, the roof overhang is often enough to shade windows. If you remember your high school trigonometry, it is possible to calculate the size (projection from the wall) of a fixed awning needed for shading windows and doors. The size depends upon the latitude of your area. As your location is farther north, the sun is lower in the sky so a larger awning is needed. If you are not a math whiz, just make a test awning from cardboard to determine the proper size for a fixed awning.
Fixed, hood-type awnings with sides are a good choice because they increase the shading period throughout the day. An adjustable awning is often the best choice because its projection can be changed with the seasons of the year and actually throughout the day if needed. Keep in mind, you probably want the sun to shine in the window during winter for free solar heating. The awning can be adjusted high enough to allow the sun’s rays in yet still provide protection from rain.
The two most common materials used for awnings are aluminum and cloth fabric. Aluminum awnings are extremely durable and, unless they are damaged from an impact, can last a lifetime. Fabric awnings are generally more attractive and offer more design, color and styling flexibility. Another advantage of fabric awnings is the adjustable ones can be lowered almost flat against the window. This provides protection from harsh weather and driving rains. Adjustable aluminum awnings typically cannot be lowered as far, but their strength provides excellent protection.
A complete archive of James Dulley’s articles on saving energy at home can be found at www.dulley.com