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
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
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