The Thermal Envelope House

The thermal envelope house proves there is more than one way to implement a passive solar design.

| March/April 1979

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A wintry day provides the perfect setting—and the perfect test—for the thermal envelope house. Sunlight reflected off snow can furnish up to 30% of the home's heating needs


An ancient Japanese proverb states that "the simplest solution is the best." If that's the case (and we think it is!), then this attractive house—nestled high in California's Sierra Nevada mountains—is one of the better solar-heated homes around, since its design allows it to store heat during the sunlight hours and release that warmth, slowly, to the interior throughout the day and night.  

In order to find out more about the unusual dwelling, MOTHER EARTH NEWS sent staffer Richard Freudenberger to Olympic Valley, California where—surrounded by several inches of snow and subfreezing temperatures—he talked to owner/designer Tom Smith (in a comfortably warm atmosphere) and questioned him on various aspects of the thermal envelope house including the all-important "passive" approach to its heating.  

The number of solar houses being designed, built, and lived in grows by leaps and bounds every year. And, more often than not, these "newcomers" on the solar scene are passively heated. Let's face it... if you're building a house from scratch, why bother with pumps and pipes (which are not only expensive, but are also subject to periodic failure) when you can get the same results from a system that uses nothing but a well-planned design to achieve its goal?

Furthermore, "active" heating systems require a collector, something that [1] most likely will be commercially produced and costly, [2] will probably detract from the beauty of the house, regardless of how aesthetically pleasing the structure otherwise is, and [3] will usually necessitate additional engineering and construction considerations.

These factors helped Tom Smith and his architectural advisor, Lee Butler of San Francisco, decide to go with a totally passive system. And—after 20 months of research and a full year of living in the house—Mr. Smith has no regrets. If anything, the structure's efficiency has exceeded his expectations ... especially since many days are overcast in the Sierras, and even in bright weather the trees native to the area block much of the afternoon sun.

The Thermal Envelope

The house is designed according to a principle Tom calls the "envelope idea." That is, the living quarters are surrounded by an envelope of tempered air. In place of a collector, a 300-square-foot greenhouse—faced with 390 square feet of double-pane, tempered glass—is incorporated into the south-facing side of the house. Behind this solarium, the structure's three bedrooms and two living areas are isolated from the outer walls and roof of the house by an inner "shell." The shell in turn is separated from the exterior by at least 12 inches of air space all around (with the exception of the east and west walls, which are common to both frameworks). This air space provides a passageway for the flow of warm air, not only creating a convective loop, but also maintaining the inner shell at a comfortable temperature (while still providing a "buffer zone" to the cooler outside shell).

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