October 16, 2006—We've heard quite a bit about using solar energy for a variety of purposes, including generating electricity and heating homes. But the sun offers another critical feature to green building: natural light. Daylighting, the deliberate, planned use of natural light in a building, is becoming more popular with residential architects as they learn about its many benefits.
Most of the research on daylighting has focused on work environments such as offices, schools and stores. The results of that research include an estimate of a 20 to 30 percent reduction in annual energy costs, thanks to reduced use of artificial lighting and less need for air conditioning to counteract the heat generated by electric lights.
Better daylighting of homes saves energy for the same reasons. But because houses are often unoccupied during the hours when natural light is most abundant, the savings would be less substantial.
Large or small, home energy savings represent only one advantage of daylighting. Studies show that natural light also produces psychological benefits. Furthermore, because a properly daylit home is more appealing to buyers, it may sell more quickly and at a better price than a house that requires extensive artificial lighting. People just simply like—and need—natural light.
Let the sunshine in
Windows are the most obvious method of bringing daylight into homes. Correct orientation and proper installation are important for maximum energy efficiency, though. Afternoon sun pouring through a west-facing window adds more heat to the house than morning sun through an east window. In areas with cold winters, windows facing southward let sun in all day long, warming the home in both temperature and mood.
Well-designed, wide overhangs—once a common feature on homes—prevent glare and excessive heat gain through windows but still allow light to enter the house. The overhangs also protect exterior views for the occupants by eliminating the need for drapes to block that heat.
Daylighting provides excellent task and ambient lighting, too. "The kitchen is the room that has the highest task volume in the house, but in typical designs it usually has the smallest ratio of daylight," says architect Steve Baczek of 3 D Building Solutions. He says that one way to make the kitchen brighter, more functional and attractive is to incorporate a pantry in the design. "The construction cost of the pantry is usually going to be less than wall cabinets, it gives better access for the client, and it frees up wall space to add windows."
Baczek cautions that windows are less energy-efficient than walls. "Even the best window is less than half the efficiency of a standard wall," he says. "The more windows I put in, the more energy dollars I’ve spent."
In fact, according to the U.S. Department of Energy (DOE), the typical house loses more than one-fourth of its heat through windows. To control this loss, the DOE recommends limiting the total window area to no more than 9 percent of the home’s floor area and choosing Energy-Star-rated windows or equivalents. The National Fenestration Rating Council provides regional guidelines for window U-factors (a measure of heat loss rate), solar heat gain coefficients (SHGC), visible light transmittance and air leakage.
