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Passive Solar: Roof Overhangs


Technology Snapshot & Benefits:

Roof overhangs are extensions off of your roof that help shade windows and walls.  These help control the amount of sunlight hitting the surfaces of your home for maximum heating and cooling efficiency in both the winter and summer.  Overhangs come in a variety of forms, from solid to louvered to vegetation-supporting, each with advantages in different areas.  There are three main types of overhangs: fixed, adjustable, and removable.  Fixed overhangs require the least maintenance and have the greatest longevity, but cannot be adjusted or removed to better suit changing sun conditions like the latter two can.  Adjustable overhangs can be expanded or condensed depending on the sun's angle, offering a great deal of flexibility and control.  Removable overhangs can easily be uninstalled and reinstalled according to your preferences, making it easier to make alterations or additions to your home.


Overhangs operate on the basic principles of solar angles.  In the summer when the sun is high in the sky, the overhang casts a long shadow over the side of your home while in the winter, when the sun is much lower in the sky, the shadow is much shorter.  This prevents the hot sun from penetrating your windows and walls in the summer and allows it to help warm your living spaces in the cold of winter.  Shutters, eaves, and awnings operate in similar ways. 


Estimated Cost Savings:

Roof overhangs can be somewhat expensive to install.  The cost of install depends on the size of the structure, the location, and whether the overhang is an addition to an existing roof or a part of a new roof.  Roofs installed as additions to existing roofs tend to be more expensive because of the extra labor and materials needed to properly attach it. 


Installing an overhang can help save on your cooling bills in the summer and heating bills in the winter.  Decreasing windows' exposure to direct summer sun can help keep your house cool without the energy expenses associated with HVAC systems.  The opposite applies during winter when the sun is able to help heat your home without turning on your heating system or lighting a fire.  This can help save a significant amount of money off of your annual heating and cooling bill.


For a less expensive alternative, consider installing shutters or an awning.  While these are not always as effective or permanent as properly installed overhangs, they provide a more affordable way to help use the sun's angle to your advantage.


Regional Issues:

Roof overhangs do not comply with all regional building codes and zoning ordinances.  Check with your local zoning committee to find out if you can add overhangs to your home. 


It is important to make sure the width of your solar overhang will provide adequate shade for your latitude.  There is no hard and fast rule for calculating the angle necessary for your home, but properly trained contractors can help you determine the proper width.  Overhangs are the most effective in areas close to the equator because of the extremely high angle of the sun creating a large shadow during hot summer months.


Installation (Getting It Done):

Solar overhangs work best when installed on the south side of your home (in the Northern hemisphere).  If they are placed on roofs that face more than 30 degrees east or west of south, they are much less effective.  The greatest heating and cooling savings will occur around midday when the sun is at its peak in the sky. 


If you are putting a new roof on your house, consider adding overhangs.  It is much easier and less expensive to bundle them into a new roofing project than to go back later and add them as additions to an existing roof.


More Information On This Topic:


U.S. Department of Energy - Energy Savers - Roof Overhangs


House Energy - Overhangs


Consumer Energy Center - Overhangs and Shading


Whole Building Design Guide - Sun Control and Shading Devices


Roof Overhangs


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