Overhangs Save Energy and Money in Your Home

Posted by lindseyshoe

Whether you are building a new home and you want it to be eco-friendly and save energy and money, or you’re interested in doing some home improvement projects to go green and save green in the long run, understanding the basics of overhangs is important.

You know that insulation is important to help maintain the heating and cooling of your home with less energy waste. Low e-coated windows play a crucial role in lowering energy cost and reducing carbon emissions, too. Overhangs are a simple, low-tech idea that can also play an important role in making it easier to heat or cool your home. How?
Basically, overhangs provide shade. Shade is a passive and effective way to reduce cooling cost. Examples of outdoor shade can include trees or shade walls covered with vine plants such as Wisteria. Another building, such as a shed, may also provide shade. Inside shade options include curtains, valences, or blinds, but these are less effective, as they deal with heat that has already entered the home, as opposed to keeping the heat out. Also in this arsenal of outside shading tools are overhangs. “Passive Homes,” which are popular in Germany and Scandinavia, use lots of overhangs to stop indoor solar heat gain.
Understanding the Value of an Overhang
The value of an overhang, whether it is a covered front porch, horizontal overhang, arbor, awning, or canopy, is called a “projection factor.” The projection factor is the ratio of distance the overhang projects from the window surface to its height above the sill of the window that it shades. The formula is A/B = Projection factor. For example, an overhang that protrudes 2 feet and is located 4 feet above a window sill offers a projection factor or 2/4 or .5.
Orientation matters, of course. The projection factor will vary depending on whether your windows are north, south, east or west-facing. For example, an overhang only 2 feet wide can shade up to 9 feet of a high, south wall in summer.
How much Energy (and Money) can you save with overhangs?
The Department of Energy estimates that overhangs or awnings can reduce solar heat gain (the amount the temperature rises due to the sun) by up to 65% on southern exposure windows and 77% on western exposures.
In hot climates, this can translate into a 26% savings of cooling energy cost and up to 33% savings in cooling energy cost in more temperate climates. In addition to saving money and energy, shading can also prevent fading of your furniture, drapes, and carpets.
Do you like to play with 3D drawing tools on the computer?
A free tool from Google can help you see the impact of overhangs. It is called Sketch-UP and is free. If you want a chance to see it before you build it, the free Sketch-Up tool may be for you.
What can you do with Sketch-Up?
You can draw a home or a single wall with a window and an overhang, and move the sun over it to represent various times of day. Other variations such as trees, shade walls, window fins, or solar sails can be added as well. It will show you the shadow patterns, both outside and inside of a building. Sketch-Up is useful for modeling sun spaces, overhangs, or greenhouses.

Users say that Sketch-Up is really easy to use. A slider bar allows you to change the time or day or time of year. Sketch-Up 7.1 was recently released.
Whether you use projection factor equations or 3D modeling tools, the value of overhangs in moderating solar gains in your new or existing home is apparent. No matter the style or color of your overhangs, you’ll be going green with these low-tech passive energy savers.