Friday, November 13, 2009

What Is A Passive Solar Design?

See that list on the right? The one titled, About Our Home? It’s pretty much the essential aspects we’ve chosen to make our home considerably more environmentally friendly than the average newly-constructed home. And I haven’t addressed anything on that list in detail yet. But that’s changing with this post. I think it’s important for you all to know a little bit more about each of these features, why we chose them and how they work to “green” our home. So, I plan on working my way down that list.

We are building based on a passive solar design, which means we kept the sun in mind at all times when planning our home. Our home is rectangular in shape and its long axis runs east/west. Our long wall will face within 30 degrees of due south. We will maximize the glass area on this south-facing wall to take advantage of the sun. Why?

Because sunlight offers us natural light. With our passive solar design, we’ll be able to rely entirely on sunlight in certain rooms for interior lighting during the day. The large, south-facing windows will allow a generous amount of light into our living and dining room. With our open floor plan, our kitchen should also receive ample daylight.

Because sunlight offers us natural heat. Solar radiation can directly penetrate our home via our south-facing windows and store within our living space (direct gain). It can also collect, store and distribute by way of a thermal mass (indirect gain). Thermal mass—or carefully-chosen materials that store heat—are key to a passive solar design. An example of thermal mass will be our flooring. A natural stone floor, such as slate, will be warmed passively by the sun during the day. At night, heat that is stored in the floor will be released back into the interior.

Because sunlight offers us natural cooling. The sun rises higher in the summer than in the winter; therefore, properly-sized window overhangs can create shading during warmer months and help to cool our home. (These overhangs are angled to permit sunlight through the windows in the winter.) Opening upper-level windows should allow naturally-rising warm air to escape as well. These elements, along with opening windows at night to let in cooler air, and closing the shades during the day, will reduce the need for supplemental cooling. In fact, we don’t plan on having a mechanical cooling system (or the energy bills that come from operating one!).

Here’s a quick run-down of passive solar design strategies (to maximize solar heat gain in winter and minimize it in summer) from the U.S. Department of Energy:

✓Start by using energy-efficient design strategies.
✓Orient the house with the long axis running east/west.
✓Select, orient and size glass to optimize winter heat gain and minimize summer heat gain for the specific climate.
✓Consider selecting different window sizes for different sides of the house (exposures.
✓Size south-facing overhangs to shade windows in summer and allow solar gain in winter.
✓Add thermal mass in walls or floors for heat storage.
✓Use natural ventilation to reduce or eliminate cooling needs.
✓Use daylight to provide natural lighting.

It takes a lot more thought to design with the sun. While our home design itself isn’t complex, it’s smart—and we owe it all to the experts. Our architects. Their knowledge of local climate, solar geometry and window technology, among other things, was mind-blowing. We learned so much just by talking with them. And I’m sure their wisdom stretches far beyond our conversations. We are forever thankful for their imparted knowledge and advice.


  1. As an architect with a passion for passive solar design, I'm pleased to see you've included this in your design criteria. Sadly, few realize how effective it is when done properly!

  2. Thanks, Josh! Our architects were major influences in our home placement. They encouraged us to choose a lot based on its sloping, south-facing design. And I'm so glad we listened!