Building the Sun Cottage

Image Gallery FIG.1 COMPLETED THREE-BEDROOM SUN COTTAGE

Follow an architect as he leads us through the planning, pouring, and pounding involved in . . .

PART VI: FINISH, INSULATION, AND BACKFILL

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 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 back in issue 67) — is architect Angus W. Macdonald. Angus developed a number of housing designs that apply low-cost building techniques to passive solar, earthtempered homes . . . and agreed to relate, in a series of articles that has now spanned six issues of MOTHER, much of what he's learned about planning and building such structures. The series has followed the actual constructionof one of the architect's standard designs . . . Sun Cottage.

By Angus W. Macdonald, M.Arch.

Through the course of the past five articles, we've talked—in some detail—about what's involved in building an energy-efficient, passive solar, earth-sheltered 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 earthsheltered, passive solar building 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, subgrade (belowground) 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 subgrade construction earth tempering, because it tends to make the building's interior temperatures more constant.