Window Shading

Shading for windows can reduce cooling costs and increase comfort while providing pleasant ambient day lighting. Shading can be produced by interior or exterior means.

• Overhangs and awnings –  These devices reduce cooling costs and improve comfort while maintaining good natural day lighting. They are most effective on south-facing windows and can be effective on east and west windows with proper design.   
• Exterior shade screens –  Shade screens can be mounted directly on the exterior of the windows. Because they reduce the amount of sunlight and radiant heat hitting the glass, they are very effective in reducing cooling costs. Screens are available with shading coefficients from 0.20 to 0.80, although screens with SC’s of 0.3 to 0.4 are the most common in Arizona.   
• Exterior louvered shades –  Some exterior louvered shade systems are adjustable so the degree of shading can be changed. Some are adjusted with motors that can be actuated with switches, timers or sun sensors.   
• Interior blinds, curtains and drapes – Light colored or reflective blinds, drapes and curtains can reflect sunlight back out of a window before it heats the space. To be effective, they must be regularly closed during the day. If they are closed consistently, they can produce significant savings. A tightly closed white venetian blind can reduce the solar heat gain through a single pane of normal glass by 25 to 30 percent¹.

¹ ASHRAE Fundamentals, 1997.

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