Roughly 40% of the unwanted heat that builds up in your home comes in through windows. Use ENERGY STAR® windows with a low  solor heat gain coefficient (SHGC) number (0.35 or lower), and avoid unshaded glass on the west side. SHGC is expressed as a number between 0 and 1. The lower a window's SHGC, the less solar heat it transmits. For natural air flow through the room, install operable windows, preferably double hung with insect screens, on opposite sides of the room -- three sides is even better. Two additional excellent methods to block heat are insulation and shading. Insulation helps keep your home comfortable and saves money on mechanical cooling systems (e.g. air conditioners and electric fans). In addition, it's important to be able to seal off and insulate the new room from the outside and from adjacent rooms. Constructing shading devices (e.g. large roof overhangs) are helpful, to block the sun. Choice of exterior building material color can also impact the heat absorption and energy costs. Dull, dark-colored home exteriors absorb 70-90% of the radiant energy from the sun that strikes the home’s surfaces. Some of this absorbed energy is then transferred into your home by way of conduction, resulting in heat gain. In contrast, light colored surfaces effectively reflect most of the heat away from your home. The U.S. Department of Energy has more information about Cooling Your Home Naturally.

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