Multiplying the vertical distance from a south-facing windowsill to the roof overhang by the appropriate “overhang factor” provides a width that combines summer shading with maximum winter sun. In this case, on site at latitude 40°, the window gets an overhang of 1 foot 7 inches through this calculation:      Vertical distance x Overhang Factor = Overhang Length     5.5 feet   x  0.29  =  1.6 feet.
Multiplying the vertical distance from a south-facing windowsill to the roof overhang by the appropriate “overhang factor” provides a width that combines summer shading with maximum winter sun. In this case, on site at latitude 40°, the window gets an overhang of 1 foot 7 inches through this calculation:
Vertical distance x Overhang Factor = Overhang Length
5.5 feet x 0.29 = 1.6 feet.

The intersection of a roof and wall is an area where seemingly minor design decisions can have a much larger effect on a home’s feel and function. At a bare minimum, an overhang must be substantial enough to prevent rain and melting snow from soaking the siding, especially at the eaves. But from the standpoint of homeowner comfort, the most important characteristic of a well-designed overhang is the ability to control the amount of sunlight and solar heat that enter south-facing windows.

Most houses benefit from sunlight in the cold winter months. Any heat gained from the sun cuts fuel bills while the natural light lifts spirits on short winter days. But while an abundance of south-facing glass may look great from the outside, it can be tough to live with: If the overhang doesn’t provide sufficient shade, the free heat that is...

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