Energy Source Builder

Turn to Solar for Lower Heating Costs

solar orientation

An energy-efficient home isn't complete until it faces the sun. Passive solar design and orientation reduces a home's heating and cooling costs and provides more spacious, well-lit and comfortable spaces.

For builders and developers, reorienting a new home to take advantage of the warmth of the sun will increase the home's appeal and marketability. It will provide that extra benefit that makes a home stand out from all the others, an added sales tool in a competitive market.

Solar Shift

Passive solar orientation places a home on the building site in such a way that the home takes full advantage of the sun's natural heat. By facing the long side of a home to the south and the short sides to the east and west, the building will capture solar heat in the winter and block solar gain in the summer. 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. If the south-facing window area reaches eight to ten percent of floor area, the home can be called "sun tempered."

A full-fledged "passive solar" home has south facing glass area of 15 to 20 percent of floor area. 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. The south wall and its windows are shaded from the high summer sun by the roof overhang.

Large expanses of west-facing glass are responsible for a considerable amount of overheating during spring and fall. East and west windows are bombarded with solar heat from the low angle sun as it rises and sets. Houses with good solar orientation also cut cooling costs by reducing wall and window area facing the blistering low angle sun.

In addition to limiting west-facing window area, you can choose window features that reduce heat gain without reducing visibility or light transmission. For most situations, windows and patio doors should have a Solar Heat Gain Coefficient (SHGC) less than 0.60 on west-facing walls. Visible light transmission should be no lower than 50 or 60 percent. (See October 1994 for more on window performance.)

Saving energy is only one of the benefits. People are simply more comfortable in a solar home that is full of natural daylight and open spaces.

Many builders and buyers believe solar site design to be an attractive option because it saves energy and increases the appeal of a home. Solar-oriented homes are in tune with the interest of many buyers.

Overcoming Hurdles

Builders often identify two barriers to orienting buildings to the south: cost and adaptability of certain building lots. However, both of these barriers are easily overcome.

Orientation is a matter of planning. Many builders and developers have found that the cost to reposition the building is really quite small. Even when home plans are changed to add more windows to the south side of a home, they are generally windows that the builder planned to include in the home anyway, so simply shifting them adds little or nothing to the overall cost.

Physical barriers to orienting a home toward the sun, such as steep slopes, conflicts with the direction of a view or existing street patterns, can frequently be overcome with proper design.

Most building lots are adaptable to solar site design. The small amount of extra effort brings worthwhile benefits to both the home buyer and the builder by adding another dimension to a home's comfort, efficiency, value and marketability.

This article appeared in Energy Source Builder #42 December 1995
©Copyright 1995 Iris Communications, Inc.