Structurally, the distinctive difference between earthbag domes and brick domes is their higher tensile strength, derived from the installation of two strands of barbed wire per row. In essence, the added tensile strength combined with the woven polypropylene fabric helps unify the individual rows into a series of stacked rings. Each of these complete rings creates a mild tensionring effect, offering tension under compression throughout the whole dome not just at a single bond beam. Excellent results have been obtained from both load bearing and lateral exertion tests conducted in Hesperia, California (see Tom Harp and John Regner,
11.21: The further the bags (tubes) are cantilevered over the underlying bags, the more they flatten out. Photo credit: Keith G.
"Sandbag/Superadobe/Superblock: A Code Official Perspective," Building Standards 62, no. 5 (1998) pg. 28). In Chapter 18 we give a condesed reprint of this article.
Functionally, the steeper the pitch is, the more quickly it sheds water. This is an added benefit in dry climates that get short bursts of violent storms. Rain has very little time to soak into an earthen clay or lime plastered roof covering.
Design-wise, the taller interior allows ample room for a second story or loft space to be included (or for a trapeze or trampoline for more athletic folk). A built-in loft can also double as a scaffold during construction. A dome also provides the most living area for the least surface area, compared to a comparably sized rectilinear structure.
Spiritually, the compass formula we use creates an arc within a perfect square. This is our personal opinion, but we have a strong feeling that the specific ratio of this shape acts as both a grounding device and an amplifier for whatever intentions are radiated within the structure. So pay attention to your thoughts.
Energy Consumption: as noted in Appendix D, a circle provides more area than a rectangle built with the same length of perimeter wall. A dome takes another step by increasing the efficiency of the ratio of interior cubic feet of space to exterior wall surface. Domes provide the greatest overall volume of interior space with the least amount of wall surface. A dome's smaller surface area to internal space ratio requires less energy to heat and to cool it. And because of the shape, air is able to flow unimpeded without ever getting stuck in a corner.
Climatically, earthen walls are natural indoor regulators. Earthen walls breathe. They also absorb interior moisture and allow it to escape through the walls to the outside, while at the same time help to regulate interior humidity. A hot, dry climate gains the benefit of walls that are capable of releasing moisturized air back into the living space. The same situation can benefit the dry interior created by wood burning stoves in a cold winter climate. Earth is a natural deodorizer and purifier of toxins. An earthen dome literally surrounds one with the benefits inherent in natural earth.
11.22: Experiment with small-scale projects before tackling a large one.
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