Superadobe

Superadobe Construction

Superadobe is a form of earthbag construction that was developed by Iranian architect Nader Khalili.[1] The technique uses layered long fabric tubes or bags filled with adobe to form a compression structure.[2] The resulting beehive shaped structures employs corbelled arches, corbelled domes, and vaults to create single and double-curved shells that are strong and aesthetically pleasing. It has received growing interest for the past two decades in the natural building and sustainability movements.

History

Although it is not known exactly how long, Earth bag shelters have been used for decades, primarily as implements of refuge in times of war. Military infantrymen have used sand filled sacks to create bunkers and barriers for protection prior to World War I. In the last century other earthbag buildings have undergone extensive research and are slowly beginning to gain worldwide recognition as a plausible solution to the global epidemic of housing shortages. German architect Frei Otto is said to have experimented with earth bags, as is more recently Gernot Minke. The technique’s current pioneer is Nader Khalili who originally developed the superadobe system in 1984 in response to a NASA call for housing designs for future human settlements on the Moon and on Mars. His proposal was to use moon dust to fill the plastic Superadobe tubes and velcro together the layers (instead of barbed wire). Some projects have been done using bags as low-tech foundations for straw-bale construction. They can be covered in a waterproof membrane to keep the straw dry. In 1995 15 refugee shelters were built in Iran, by Nader Khalili and the United Nations Development Programme (UNDP) and the United Nations High Commissioner for Refugees (UNHCR) in response to refugees from the Persian Gulf War. According to Khalili the cluster of 15 domes that was built could have been repeated by the thousands. The government dismantled the camp a few years later. Since then, the Super Adobe Method has been put to use in Canada, Mexico, Brazil, Belize, Costa Rica, Chile, Iran, India, Siberia, Mali, and Thailand, as well as in the U.S.

Methodology

Materials

Many different materials can be used to construct Superadobe. Ideally you would have earth or sand, cement or lime, and Superadobe polypropylene tubing (available from Cal-Earth or other suppliers); bags can be polypropylene, or burlap. What is important is that they are UV resistant or else quickly covered in plaster. Virtually any fill material will actually work including un-stabilized sand, earth, gravel, crushed volcanic rock, rice hulls, etc. If the fill material is weak the bags have to be really strong and UV resistant, or else plastered right away. The material can be either wet or dry, but the structure is more stable when the tube's contents have been moistened. Other materials needed include water, shovels, tampers, scissors, large plugs or pipes (for windows), and small buckets or coffee cans for filling the sacks. If you decide to go the quicker way, then electric or pneumatic tampers can make the tamping easier, electric or gas powered bucket chain that can reach 7 metres (23 ft) or higher would eliminate the need of manual filling of sacks or tubing using coffee cans or small pails.

Process

The foundation for the structure is formed by digging a 12” (approx. 30 cm) deep circular trench with an 8’-14’ (approx. 2 to 4m) diameter. Two or three layers of the filled polypropylene sand tubes (superadobe tubing) are set below the ground level in the foundation trench. A chain is anchored to the ground in the center of the circle and used like a compass to trace the shape of the base. Another chain is fastened just outside the dome wall: this is the fixed or height compass and gives you the interior measurement for every single layer of superadobe bags as they corbel ever higher. The height compass is exactly the diameter of the dome. The center chain/compass is used to ensure the accuracy of each new superadobe layer as it is laid and tamped. (The compasses must be made of non-stretchy material to ensure an accurate geometry.)

On top of each layer of tamped, filled tubes, a tensile loop of barbed wire is placed to help stabilize the location of each consecutive layer: it plays a crucial role in the tensile strength of the dome - it is the 'mortar'. Window voids can be placed in several ways: either by rolling the filled tube back on itself around a circular plug (forming an arched header) or by waiting for the earth mixture to set and sawing out a Gothic or pointed arch void. A round skylight can even be the top of the dome.

It is not recommended to exceed the 14’ (4m) diameter design in size, but many larger structures have been created by grouping several "beehives" together to form a sort of connected village of domes. Naturally this lends itself to residential applications, some rooms being for sleeping and some for living. There is a 32' (10m) dome being constructed in the St. Ignacio area of Belize, which when finished will be the centre dome of an eco-resort complex.

Finishing

Once the corbelled dome is complete, it can be covered in several different kinds of exterior treatments, usually plaster. Khalili developed a system that used 85% earth and 15% cement plaster and which is then covered by “reptile”, a veneer of grapefruit sized balls of cement and earth. Reptile is easy to install and because the balls create easy paths for stress, it doesn't crack with time. There are many different possibilities. Some Superadobe buildings have even been covered by living grass, a kind of green roof but covering the entire structure. Any exterior treatment and building details would need to be adapted to a region’s specific climatic needs.

Emergency shelters

According to Khalili's website, in an emergency, impermanent shelters can be built using only dirt with no cement or lime, and for the sake of speed of construction windows can be punched out later due to the strength of the compressive nature of the dome/beehive. Ordinary sand bags can also be used to form the dome if no Superadobe tubes can be procured; this in fact was how the original design was developed. There is a great potential for long-term emergency shelters with Superadobe because of the simplicity of construction. Labor can be unskilled and high physical strength or formal training is unnecessary for the workers, so women and children are able to substantially contribute to the construction process. Local resources can be used with ease. Superadobe is not an exact art and similar materials may be substituted if the most ideal ones are not readily available.

In an interview with an AIA (American Institute of Architects) representative, Nader Khalili, super adobe’s founder and figurehead, said this about the emergency shelter aspects of Superadobe:

A 400-square-foot (37 m2) house, with bedroom, bathroom, kitchen, and entry — I call it the Eco-Dome — can be put up in about four weeks, by one skilled and four unskilled people. Emergency shelters can go up much more quickly. After the Gulf War, the United Nations sent an architect here. We trained him, and he went to the Persian Gulf and put them up with refugees as they arrived at the camps. Every five incoming refugees put up a simple structure in five days. It's emergency shelter, but if you cover it with waterproofing and stucco, it will last for 30 or more years.

Bibliography

See also

References

  1. ↑ "Superadobe - What is Superadobe?". Calearth.org. Retrieved 2012-10-13.
  2. ↑ "Green Home Building and Sustainable Architecture: A Short History of Earthbag Building". Greenhomebuilding.com. 2007-08-18. Retrieved 2012-10-13.
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