Essential Earthbag Construction by Kelly Hart

Author:Kelly Hart
Language: eng
Format: epub
Publisher: New Society Publishers
Published: 2017-05-09T04:00:00+00:00

In that experiment, I really wanted to somehow make the ellipse work, so I devised a rigid framework with wooden poles, steel cable, and a steel hoop at the top of the dome that served as an armature for maintaining the shape that I wanted. Without this stiff armature supporting the dome, it would not have been stable and would likely have collapsed! So now I always advise folks to stay with circular domes for safety’s sake.

The second rule is that earthbag domes cannot be truly hemispherical without some rigid framework to serve as an armature. I have seen hemispherical earthbag domes built over a geodesic framework, and that worked out fine. But without the framework, such a dome could become unstable during construction, particularly as the top of the dome is approached. Earthbags simply cannot be relied upon to support themselves when formed into such a relatively horizontal shape at the top.

The strongest and preferable shape for an earthbag dome is often referred to as an inverted catenary arch. Such an arch is sometimes described as the shape that a chain will naturally take when it is suspended between two fixed points and allowed to hang. If you take this shape and invert it, you have the ideal shape for the cross-section of a dome.

This catenary shape can be approximated in various ways, similar to the ways described in Chapter 7; that is, you make a guide to describe the arc of the walls. Above loft level, I have often used a simple cone shape based on an equilateral triangle — with 60 degree angles at the base — to fashion the upper part of the dome. This has the advantage of creating more potentially usable standing space in a loft area. Figure 7.10 shows this arrangement.

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