Lloyd Alter
DCL
It is really remarkable how the simplest and most obvious technologies for saving energy, keeping cool in summer and warm in winter, have just been forgotten or ignored. After all, the builder would rather sell you a ground source heat pump than design in clever passive technologies because they are free and heat pumps aren't. But you might not need the heat pump if you get the roof overhangs right and take advantage of passive heating and cooling techniques.
The sun is higher in the summertime; that is why it is summer, as it is closer to perpendicular and we get that much more solar radiation. If you design your roof overhangs and your windows properly, you can take advantage of the different sun angles to keep the heat of the sun out in summer and let it in, for passive heating in winter. It is solar 101.
But there is a mathematical relationship among roof overhang, roof slope and soffit height; architects and designers have traditionally been more concerned about getting the aesthetics right rather than the solar angles. Frank Lloyd Wright's shallow sloped roofs and deep overhangs have been out of fashion for a while, losing out to faux Georgian and Builder McGable style. So it is a little more work, a little harder to design, but you can calculate the right angles and lengths with tools from Sustainable By Design and mre design tools can be found at Builditsolar. The Office of building Technology of the US Department of Energy has a good tool in a PDF here.
If you are already in a house or apartment, there are things you can do to get the same effect without tearing off your roof and starting over. You could add on a pente eave over your first floor windows; you can add awnings or light shelves. There are lots of methods of doing that one low-tech thing: Let the sun in for winter, keep it out for summer.
