The Thermal Envelope Home Redesigned

The controversial thermal-envelope house is reconsidered and redesigned to make use of the features that work and eliminate those which don't.

| July/August 1983

thermal envelope home redesigned

 Steve and Tamara McKinney's dwelling in Squaw Valley, California exemplifies Smith's evolved design. It has an attached solarium and earth-coupled foundation, but no envelope, superinsulation, or excess thermal mass.


In March of 1979, MOTHER featured a story on what was at that time a rather unusual passive solar house. For instead of collecting warmth and storing it in a conventional medium, this double-shelled maverick admitted insolation into a greenhouse and then routed the sun-tempered air—by convection—through a vertical loop that completely surrounded the living area. During its circuit, the air gave up its heat to the mass of the inner structure, and then, when it had cooled, it was reintroduced to the solarium to be warmed anew. 

In effect, the envelope of heated air not only tempered the living quarters, but also provided a buffer zone between the harsh outside climate and the moderate atmosphere within the house, while the home itself functioned as both collector and storage medium. 

The structure worked, but many people—including Tom Smith, the dwelling's owner, co-designer,and the author of this article—had difficulty pinpointing exactly why. Consequently, it wasn't long before the design was called into question by individuals knowledgeable in the solar field. But by the same token, proponents of the "cause" were equally ready to defend double-shell architecture, and did so. In the meantime, various hybrid designs rooted in the envelope theme were unveiled, and they, too, functioned well. 

While all this was going on, though, Smith merely observed quietly, and then got busy working out the modified structure shown in the photos, based on the knowledge he'd gained in the several-year interim. Since Tom was one of the first to promote the original double envelope concept, we think it only fair to give him an opportunity to explain what his new design is all about, and why it differs from the old one. 

I've had a tiger by the tail ever since my "thermal envelope" home appeared in MOTHER EARTH NEWS over four years ago, and to me it's ironic that what was intended to be an expression of simplicity turned instead into a source of confusion and controversy! 

Those not familiar with the course of events should know that a lot of people initially thought my double-shelled house wouldn't work. Then, when the house itself proved otherwise, folks agreed that it indeed worked, but no one could figure out exactly why. Finally, the solar "experts" got into the discussion. As a result, the theories and research became more sophisticated, but the obvious seemed to become more obscure. The field even polarized into camps of advocates and critics! 

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