Question

We want to design a passive-solar home for a hot climate. Can we still have views to the east?

Asked by Dorothy Shannon, Charlotte, NC

On the lot where we're building our new home, the best views are to the east. Is there a way to orient the house to enhance the effect of the sun and give us natural light all day without losing those views? The builder blanched when I said I wanted windows facing south—he says the sun will melt the furniture. I gather passive solar isn't popular in hot climates. Should I give up on the idea?

Answer

Greg Upwall

Answered by Greg Upwall

Washington, DC

Studio Upwall

February 4, 2008

Definitely do not give up on the idea! Passive design for heating, cooling, and daylighting can and should be incorporated into buildings in all climates.

These passive solar strategies have been used around the world for centuries, and it is only in the past 60 years, since the advent of mechanical heating and air conditioning systems, that we have become dependent on artificial temperature control and abandoned common sense, low-tech strategies to keep buildings comfortable.

Since you live in a hot and humid climate, your primary concern is allowing adequate daylight (indirect sunlight) in while shading the house from undesirable direct sun.

The house should be designed as a unique response to the surrounding geography, but here are some general principles to follow.

Windows and direction of exposure

First of all, window openings and overhangs should be designed for each wall according to the direction of exposure:

North-facing walls. The north side of the house is the place for large windows and shallow overhangs. This is the "guilt-free" stuff; windows will provide natural light without the direct solar heat gain.

East-facing walls. If you want to take advantage of views to the east, larger windows with deep overhangs are appropriate here. It is sometimes okay to allow the early morning sun to directly enter the house, especially in a kitchen or breakfast nook. The overhangs should be deep enough, however, to start shading the windows by about 9 a.m. during the summer.

South- and west-facing walls. Here you will want small windows set high in the wall, with deep overhangs. The depth of the overhang should be set to shade all direct sun from entering during summer months. Deciduous trees should be planted at these walls because they will provide shade in summer, but allow sun to filter through during the winter when they drop their leaves.

Overhangs

Perhaps the single most important factor in passive solar design for hot climates is providing the proper depth of overhangs for shading.

  • The depth should be based on the extreme summer and winter sun angles for your latitude.
  • The overhang should be deep enough to shade all or most of the direct sun in the summer while allowing some sun to enter the house in the winter months (when the sun is lower in the sky).

Overhangs are most commonly roof eaves that extend out over the tops of walls. Canopies, such as a wooden trellis over a window, are another option. Overhangs should be built from materials that will block the sun and the heat (Canvas is not ideal, as it does not have any thermal mass). Another important shading device is commonly referred to as a light shelf. This is a solid canopy that projects at the two-thirds point of the height of the window, shading the portion of glazing below the shelf, while at the same time reflecting light up into the ceiling space through a transom window placed above the shelf. (Reflected light does not bring nearly as much heat gain as direct sunlight.)

Insulation, ventilation and other factors

There are several other factors that should be considered in passive design for hot climates.

  • Walls should have adequate thermal mass and be well insulated to prevent heat infiltration.
  • The roof should be lighter in color, well insulated, and equipped with proper ventilation to exhaust acquired heat.
  • Natural ventilation should be provided through large operable windows on opposite walls. The width of the house should allow for windows on each side to promote cross-ventilation: in general, a long, narrow footprint might be best in order to avoid vast interior spaces that cannot be adequately ventilated.

Another efficient cooling strategy that uses little energy is a whole-house fan. Instead of attempting to beat the heat by pumping refrigerated air into the house, the principle behind the whole-house fan is to effectively dissipate the heat as it builds up inside the house. Whole-house fans are typically installed in the attic or at the highest point of a vaulted ceiling. Since they are high-volume fans, they are able to evacuate the heat from the space quickly and therefore only run at brief intervals during the hottest part of the day.

 

For more information:

Read Cynthia Phakos's Ask A Pro, "How can I remodel my oceanside property for maximum energy efficiency?" for more information on designing homes for hot climates.

Read Cassandra Adams's Ask A Pro, "Are whole-house fans effective in northern latitudes?" for more information on whole-house fans.

Tagged In: passive solar, summer energy, whole house fan, daylighting

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