Building a Passive Solar Home: Part VI

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Fig. 2, normal construction versus earth-sheltered construction.
Fig. 2, normal construction versus earth-sheltered construction.
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Fig. 1, the completed three bedroom, passive solar home.
Fig. 1, the completed three bedroom, passive solar home.
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Fig. 4, completed section of the Sun Cottage.
Fig. 4, completed section of the Sun Cottage.
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Fig. 3, insulation and waterproofing.
Fig. 3, insulation and waterproofing.

All too many of us have found that building an energy-efficient home seems to be a dream . . . a fantasy that’s kept just out of reach by escalating prices and high interest rates. Of course, MOTHER EARTH NEWS has long been exploring ways of breaking this vicious circle of waste, and one inventor of solutions–whose work we’ve shown you before (starting with Building the Sun Cottage Part I: Site Selection)–is architect Angus W. Macdonald. Angus developed a number of housing designs that apply low-cost building techniques to passive solar, earth-tempered homes . . . and agreed to relate, in a series of articles that has now spanned six issues of MOTHER EARTH NEWS, much of what he’s learned about planning and building such structures. The series has followed the actual construction of one of the architect’s standard designs . . . the Sun Cottage.

Through the course of five articles, we’ve talked–in some detail–about what’s involved in building an energy-efficient, earth-sheltered, passive solar home. Thus far, however, we’ve touched only lightly on the theories upon which such a structure’s performance is based. Consequently, in this, the final installment of our series “Building the Sun Cottage”, we’re going to pay particular attention to the proper detailing that makes the various heat-exchange systems in an earth-sheltered, passive solar home work. Then we’ll wrap up with that most crucial of all earth shelter components: waterproofing. The appearance, thermal efficiency, comfort, and longevity of the Sun Cottage are all quite dependent on how the structure is finished, so the final stages are perhaps the most important!

Heat Movement

The masonry walls and concrete floor slab of our building–those large surface areas surrounding the living space–provide great thermal inertia. . . a term that refers to how slowly a mass reacts to temperature change. Heat is stored in the mass and is later radiated gently and evenly into living areas, which is one reason why the Sun Cottage doesn’t require a mechanical (or active) system to distribute stored energy.

Likewise, sub-grade (below ground) masonry areas conduct heat to and from the relatively thermally stable earth surrounding the walls. In fact, the ground around an earth shelter changes temperature so slowly that areas eight feet or more below grade are actually warmer during winter than they are in summer. What’s more, the overall range of this variation is usually less than 10°F. We call the shielding effect of sub-grade construction earth tempering, because it tends to make the building’s interior temperatures more constant.

  • Published on Mar 1, 1984
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