UNIT ONE BEAUTY AND FUNCTION

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HANG ON TO WHAT YOU'VE GOT ...

It's impossible to build and maintain an energyefficient house without proper insulation, and the Balcomb home is no exception to this rule. The thermal mass wall — which serves as the dwelling's nighttime heater — is also (in effect) an insulator: The wall's heat transfer function prevents it from having any significant heat loss ... since the outer surface losses are turned into inner surface gains. The building's east and west walls, however—which are also constructed of adobe — are more directly insulative. Though their mass does tend to delay inside temperature changes — just as does the greenhouse wall-they don't transfer any significant amount of solar heat to the home's interior.

The north-facing wall is buried below ground level to a depth of four and a half feet. This subterranean portion is built of eight-inch concrete blocks (with the cells filled for extra insulation) and is sealed with plastic roofing cement and two inches of rigid polystyrene. Above ground level, the northern wall consists of a stucco-covered frame of 2" X 8" studs on 16" centers ... and is insulated by a 1-1/2" layer of fiberglass batt, a vapor space, and then six more inches of fiberglass batt. Three inches of urethane foam in the roof complete Unit One's insulation package.

..AND GET AMAZING THERMAL STABILITY

There is a popular misconception that life in a passively heated solar home involves some compromises ... such as donning and shedding clothing as the weather changes, lighting fires for extra warmth, etc.

Sara Balcomb, however, has a bone to pick with such "myths": "I believed all that myself," she says, "until I lived through a winter in my passive home." And Dr. Balcomb's careful records of year-round temperatures in Unit One certainly show that the supposed necessity for compromise is indeed a myth ... at least in this particular solar abode.

The dwelling's thermal mass wall and insulation—combined with its 20% active storage capability -conspire to keep Unit One's inside temperature incredibly stable. During the month of December 1977, for instance, the Balcombs' living area's temperatures varied by a grand total of 40: from 67°F to 71°F.

Sara claims that it takes about two days for the house to react to a change in weather, and that there is never more than a 50 swing in any 24-hour period. The actual recorded extremes for the house are a low of 65°F in February (limited by the electric baseboard units, which are thermostatically controlled at 65°F) and a high (A 76°F on a 97°F summer afternoon. And, as Sara points out, "A variance of 21° is hard to achieve even with conventional air conditioning ... but we did it simply by natural means."

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