Overhangs: A cool idea?
We all know windows are great for letting light in buildings to brighten up dark corners. The problem is during the summer it also lets in so much heat through the solar heat streaming through the windows heating up the flooring and everything else thing inside. During the winter, this extra heat is considered a bonus. Some of the quaint houses built in the 1950’s had awnings over some or most of the windows that at least faced the equator. This wasn’t just for aesthetics, this was a practical application.
Overhangs can block those warming rays from the sun and shade areas of the house to keep them from getting hot during those blistery days. They can be built over windows like awnings and covered porches. But what if we considered using roof as an overhang to shade the house? Its already used as a shade for the interior of the house, if extended, it could even shade the windows and most of the walls of the house. This would lower the outer temperature of the wall that could radiate heat through to the inside.
Too much of a good thing can’t always work out for the best. If the over hang is too large, then you will get too much shading coming in your windows during the winter and then loose out on some of that solar heat. Luckily, the great people at Sustainable By Design have a few calculators to help you out with such a problem. Click here for the calculator to see just how large of an over hang that you would need. Also, click here to calculate how much light or shading that the overhang would allow through out an entire year.
The way they calculate the size of the overhang is by the angle of the sun according to your latitude. This is then adjusted to the time of the year and your preference of more or less shading during the winter.
Overhangs are not effective on east or west facing windows because the sun is too low in the morning and afternoon for an overhang to provide any effective shade. Some form of external screen, trellis, or landscaping will be the only effective solution. On south facing windows, they are only effective in blocking direct sun.
In looking at the solar radiation numbers for a few locations, it appears that only about half of the radiation arriving at a window is direct solar radiation. The rest of the radiation is diffuse sky radiation and reflected radiation from the ground. So, while overhangs are quite helpful, they will still let though this half of the solar radiation.