The Sunburst Passive Solar House

This truly attractive passive solar house—designed around an honest-to-goodness Trombe wall—represents the "state of the art" in (ultra) low-technology solar heating.

055 passive solar house 01 cover.jpg

The Sunburst passive solar house is as attractive (if not more so) than any conventionally heated structure both inside and out.


Content Tools

Anyone who's familiar with solar-heated houses knows that there are any number of ways to harness the sun's energy, from the simplest "passive" approach (the "little guy's" method) all the way up to the expensive, highly technical, "active" systems that big business tends to promote.  

Recently, one of MOTHER EARTH NEWS' staffers and a photographer went to Landenberg, Pennsylvania to look at one of the "simple" systems and to talk to its designer—produce salesman-turned-builder Jim Kries—who is in the process of constructing a small community of passive solar houses; he calls them, very appropriately, "Sunburst" homes.  

Mind you, though, these houses don't utilize what you might call your "average" solar collector. Instead, Jim has opted to incorporate a "Trombe wall" (named after its inventor, French physicist Felix Trombe), which not only heats the house without any moving parts or expensive equipment,

but makes the dwelling as attractive (at least!) as any custom-built conventional home. In fact, the owners of the house—Vincent and Kathy Polidoro—decided to buy it when they saw the blueprints before construction of the home had even begun. And, after talking to the Polidoros, we're convinced that they haven't been disappointed at all!  

It's no secret that solar-heated dwellings have come into their own in the past decade or so, thanks largely to the efforts of many "unconventional" yet dedicated designers. Folks like David Wright, William Shurcliff, Steve Baer, Bruce Anderson, and a host of others saw a definite need to "make hay while the sun shines" rather than just sit around and complain about the rising costs of fossil fuels.

And there's no doubt that these solar homes really work despite what the skeptics say about cloudy days, winter storms, and other "no-sun" situations. But with a few exceptions, most effective solar homes aren't as attractive as their designers or the public would like them to be. Let's face it, there's not too much you can do to improve the looks of a solar collector without lowering its efficiency. Until now that is, because the Jim Kries-designed "Sunburst" solar house is a real beauty!

You see, instead of trying to "hide" the collector in the back yard, Jim decided to use it as the entire south wall of the ground floor. To do this, he built a 14-inch-thick, 225-square-foot "Trombe wall" which is painted black on its outer surface (to absorb and hold the sun's heat) and is finished in white stucco on the inside (to assure an attractive, light, "airy" look in the house's dining and living room areas).

Of course, this "collector wall" isn't directly exposed to the weather. Instead, the entire surface is faced with another 225 feet (or so) of 5/8-inch-thick insulated glass, which is mounted from floor to ceiling about six inches in front of the actual collector. The double wall creates a passageway for the heated air to follow. And, as Kries is quick to point out, that insulated glass—although it is expensive—is no more so than common replacement panes for sliding doors because that's exactly what it is! In other words, instead of using fancy solar hardware where it's not needed, Jim "made do" with standard building materials to reduce costs and to insure that replacements would be available in the event of accidental damage.

So what we have, then, is a low-cost, simple way of collecting and storing heat ... which is great in the winter. But what about the summer? Well, Jim has that one figured out, too. The south-facing upstairs wall (the one which is above the Trombe wall) is cantilevered three and a half feet beyond the glass "wall" below it. This overhang effectively protects that expanse of glass from the rays of the high summer sun; if the sun can't get to the glass or the black wall behind it, no heat is produced. Also, most of the rays that do find their way to the collector surface just "bounce off", because of the oblique angle at which they strike the glass.

To insure that the house is completely free of unwanted hot air in the summer, Kries installed a large attic fan in the dwelling's second-story roof. Though he doesn't foresee a need for this addition, Jim explains that the fan serves as a positive "warm air exhaust route", which might be needed in the event of unusually hot or humid summer weather.

Supplemental Heat ... Just in Case

The Trombe wall—despite its size and mass—still can only provide about 60 to 75% of the house's total winter heating needs (an impressive percentage, considering the low-cost simplicity of the system). Therefore, Jim added two auxiliary heat sources,which-he hopes won't ever see much use.

The main "backup system" is a 98,000 Btu/hr., thermostat-activated, oil-burning hot water furnace which, because it's a two-zone design ("two-zone" means that the temperatures of two different areas can be controlled separately), only supplies heat where it's actually needed. Although the furnace is capable of providing all of the heat that would ever be necessary, Kries hopes that it will only be used on the coldest of days. The thermostats are set at 55*F, and thus far—says the builder—the furnace has not had to come on.

In addition to this "conventional" source of heat, Jim also makes use of an attractive Morso 1125 wood burning stove ... a unit that's not only favored for its high Btu output, but because it can also be converted into a fairly efficient "open fireplace" by removing the doors. And, since the Sunburst house is located on two wooded acres, fuel supply should be no problem.

Insulation Makes the Difference

Jim was determined to make his design as energy efficient as possible, and that meant using insulation to its fullest potential. To accomplish this, Kries framed the entire structure with 2 X 6's on 24-inch centers (instead of the usual 2 X 4's). This gives the house a rocksolid framework and allow a greater-than-usual amount of insulation to be used. Jim took advantage of this extra space, too. He installed six-inch fiberglass batting (over one-inch styrofoam sheeting) in the walls, and nine inches of batting in the ceiling.

In addition to insulating the walls and ceiling to the limits (they have R-values of 24 and 30 respectively), Kries also paid special attention to the foundation of the house (the 16-inch-thick "solar slab") by first laying down a full inch of tongue-and-groove styrofoam. This material was covered with six inches of gravel, which in turn was topped with six more inches of concrete. Finally the foundation was finished off with 3 inches of brick veneer, which serves as the floor of the living room. Not only does this "layering" prevent cold from seeping in through the foundation, but it also stores warmth within the mass of the floor. . . which works in concert with the Trombe wall to hold collected heat and release it slowly. (The Trombe wall is mounted directly on the insulated "solar slab" foundation of the house ... which also supports the masonry chimney in the center of the building. In this manner, both the heat collected through the Trombe wall and that absorbed by the chimney via the fireplace are held inside the entire structure for up to 16 hours).

But the high insulation factor isn't the only thing that keeps heat within the house. Jim has made clever use of "airlock" double-door entryways (a fancy way of describing old-fashioned vestibules). He also relies on several south-facing windows to admit heat (and light) into various rooms in the house, including the living/dining area behind the otherwise solid Trombe wall.

Building and Maintenance Costs