Although it is best to face the home directly into the sun, it can be oriented up to 30 degrees away from due south and lose only 5 percent of the potential savings. There are some physical constraints, such as steep lots, shading from buildings and trees, and existing street patterns, when orienting a home on a lot. However, the 30 degree flexibility makes it much easier for builders to think about solar orientation when siting a home. While there is no need to change the house design, moving windows to the home's south side will enhance its solar performance. With this much glass, additional features must be added, such as thermal storage mass and summer shading.
Many builders choose to keep the project simple by sticking to the sun-tempered level.
Solar Performance Research supports the energy savings claims of passive solar designers. A study by the Bonneville Power Administration placed home space heating savings between 10 and 20 percent and a study by the City of San Jose, California estimated savings for cooling costs between 10 and 40 percent. The homes in both these studies were simply reoriented to the sun and did not include any special solar design features. It's not surprising that proper orientation increases heat gain in winter and saves money by reducing heating bills. However, homes with good orientation also save money on summer cooling.