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How Earthbag Homes Work


Earthbag Construction
This earthbag home has a wooden door form and wagon wheel window forms.
This earthbag home has a wooden door form and wagon wheel window forms.
Kelly Hart/Courtesy www.EarthbagBuilding.com

Earthbags can be used as infill for a more conventionally framed home, but for this section, we'll look at how to build an earthbag dome.

Rubble trench foundations, meaning a trench filled with rocks, gravel or broken concrete, are commonly used with earthbag homes. The first layer of bags can either be placed at ground level or slightly below ground level, in the trench.

Bags should be filled on-site, right before they are placed. Earthbags can be filled in several ways. For example, some builders have constructed bag stands that hold a big bag upright so that a person can shovel soil into it. As the walls get higher, bags could be lifted in place partially filled and then finished by handing up cans of dirt.

As bags are filled, they can be sewed closed with twine, but this isn't required. An alternative would be to place the open end of the bag, folded in with neat corners, against the sealed end of the adjoining bag. Tightly placing the bags keeps them closed and ensures the wall's structural strength. Bags should be placed so that the places where the bags on the previous row meet are covered by the bags on the subsequent row, just like brickwork.

After a row of bags has been laid, the tamper presses the bags down into place. This keeps the earth from shifting and keeps each layer level. This compression is also what forces the dirt inside an earthbag to become a solid, self-supporting form, so that if the bag were somehow removed, the dirt wall would still stand. Between each layer of bags, place one or two strands of barbed wire along the top of the row to hold the next row of bags in place. Even if the barbed wire pokes a hole in the bag, the tamping of the dirt ensures that the wall remains solid; large holes can be patched with duct tape.

To add windows and doors to the structure, use wooden forms to mark the place where the window or door will be, and then place earthbags around it. It may be necessary to create custom bags by using varying amounts of dirt. For example, fan bags are used to put arches over the windows or doors.

Plastering an earthbag home
Plastering an earthbag home
Kelly Hart/Courtesy www.EarthbagBuilding.com

The bags are gradually stepped in to build the dome. A simple homemade compass or tripod guide can aid in positioning the bags of the dome. One such compass could consist of a pole placed in the center of the floor. At the top of the pole, an L-shaped piece of material can be attached with an adjustable clamp. Rotating the pole and adjusting the metal inward will help evenly place bags. As a general rule, earthbag builders Kaki Hunter and Donald Kiffmeyer recommend stepping in a maximum of one-fourth the width of the previous bag to maintain structural integrity. In other words, a builder working with 12-inch (0.3-m) bags would step the next layer in about 3 inches (7.6 cm), so that the other 9 inches (22.9 cm) are still resting on the previous layer.

When complete, the structure should be plastered as soon as possible to avoid prolonged exposure to the sun. Mud plasters are most commonly used on earthbag structures, but lime and cement plasters may also be used if you place a mesh over the bags to hold it in place. A roof can be finished with coverings such as shingles or tiles if desired.

Before you start piling earthbags pell-mell in your backyard, learn the challenges of earthbag construction next.