In typical earth-sheltered home kits, the dome's structural members are bolted together on top of a preformed slab.
PHOTO: MOTHER EARTH NEWS STAFF
Financing, contract labor, and raw materials costs have taken their toll of the American own-your-own-home dream in recent years. At the same time, in an effort to seek a new, energy-saving route indoors, many people are now considering housing alternatives that once were shunned by society's mainstream.
Unfortunately, "more efficient" doesn't always mean "less expensive". Take earth-sheltered housing, for example. A decade ago, few folks had ever heard of it, and even fewer understood its advantages. Today, though, soil-covered structures number in the thousands and appear in a variety of styles and sizes. Even so, these subterraneans share one common drawback: All of them must be specifically engineered to withstand the pressures that their earthen blankets invariably subject them to . . . and in many instances, this has required the services of a professional architect and the use of some downright serious structural components.
Well, that may be within the reach of folks who have husky financial resources, but shoestring budgets aren't designed to handle that kind of load. There's no easy way around the dilemma, either. Regional and local building codes universally demand approved engineering on earth-bermed construction for the protection of the residents-to-be . . . effectively quashing any do-it-yourself shortcuts contemplated by the greenback-strapped owner.
Situations such as this beg for solutions, and we've recently heard of an ingenious one you might want to look into: A firm by the name of Earth Systems, Inc., markets a pre-engineered structure that it sells in earth-sheltered home kits. This package differs in at least four ways from the other prefab homes currently available. First of all, it's truly an earth-sheltered design and thus incorporates all the advantages inherent in that kind of building. Second, it's in the shape of a hemispherical dome, which offers an excellent strength-to-material ratio and is freestanding, with no internal supports. Third, the structure is composed of an integral steel framing network covered with a shell of concrete (this monolithic construction eliminates problem seams and joints). And finally, you can purchase the kit shipped complete from the factory, or—if local purchasing of some materials seems more attractive—you can send for part of it and supplement the rest at the building site.
Earth Systems offers an oval dome and a half-dome (open end) structure, as well as the "true" dome shape . . . and their standard kit comes in four sizes with diameters of from 30 to 52 feet. The form is established with a frame of lightweight bolted-together steel beams to which is attached a network of 1/2" reinforcing bar to create a grid of 12" squares. Then a fabric-and-wire panel is fastened to this skeleton, and a 4"-thick covering of concrete—shot from a pressurized gun—is applied to the surface of the structure, with additional material being supplemented at the base. Once that's set, insulation and waterproofing can be added to the outside, and—after a sufficient curing period—the excavation can be back-filled and the house can be covered.
When compared with conventional stud-frame construction, this technique offers a considerable savings in hourly labor costs. In fact, it's possible to completely close in a 1,950-square-foot dome—on an unexcavated site—in a week's time . . . a process that more than likely would take a carpentry crew three times that long!
Because of the shape of the structures, most Earth Systems homes are designed and built as two-story units. The grade-level entry is on the second floor, where (typically) the kitchen, dining area, and family room are situated. A circular stairway offers access to the below-ground level, which features a vaulted living room and standard ceilings in the bedrooms and bathrooms. Each of the subterranean rooms has an atrium that provides natural illumination, ventilation, and emergency egress, and an above-ground cupola at the top of the dome admits additional daylight and outside air as desired.
Ordinarily, only the lower half of the dome is actually below grade, while the upper portion is bermed with earth to a depth of two feet or so. But Earth Systems' structural engineer states that the entire building has been designed to accommodate full embedment if need be, because the framework is stressed for just about any type of construction site that can be imagined. The dome's spherical shape helps to distribute weight evenly over its surface. Loads on the upper part of the shell are compressive and translate into tensional forces at the base. There, the footing serves both as a foundation and as a stabilizing ring to keep "stretching" pressures in check.
The basic kits—which include the structural beams, their anchors, the necessary supports for the second floor, the rebar, the fasteners, and the forming material—cost between $10,500 and $15,000, depending on the size of the house. Obviously, by the time the structure is finished inside and out, the total bill will come to considerably more than that figure . . . but the owner-builder can tackle a great portion of the labor, thus appreciably cutting those costs. Also, conventional financing has been approved for these designs. Indeed, the Earth Systems folks indicate that none of their structures has ever been denied a building permit, though their houses have been constructed in a number of states from coast to coast.
Spherical, subterranean, and economical . . . that may sound like an unusual combination. But it might just be the solution if you're going to build on a "pay as you go" schedule . . . particularly if you'll have to squeeze in your carpentry around the old nine-to-five haul.