Super Adobe
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Super Adobe is a form of Earthbag Construction that was developed by Iranian architect Nader Khalili. The technique utilizes long snake-like sand bags to form a beehive shaped compressive structure that employs arches, domes, and vaults to create single and double-curvature shell structures that are strong and aesthetically pleasing. It has received growing interest for the past two decades in the Natural building and Sustainability movements. Due to Super Adobe’s inexpensive nature, ease in construction, and use of locally available materials, it has also been proposed for use as a long term emergency shelter. Super Adobe is also known as Superadobe (one word), and Superblock.
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[edit] 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 more peaceful 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 Super Adobe 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 Super Adobe 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. Unfortunately the government dismantled the camp a few years later. since then, the Super Adobe Method has been put to use in Mexico, Brazil, Chile, Iran, India, Siberia, and Thailand, as well as in the U.S.
[edit] Methodology
[edit] Materials
Many different materials can be used to construct Super Adobe. Ideally you would have barbed wire, earth or sand, cement or lime, and Super Adobe fabric tubing (available from Cal-Earth), but the bags can be polypropylene, burlap, or some other material. 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.
[edit] Process
The foundation for the structure is formed by digging a 12” deep circular trench with a 8’-14’ diameter. 2-3 layers of the polypropylene filled sand tubes (Super Adobe fabric tubing) are set below the ground level in the foundation trench. A rope is anchored to the ground in the center of the circle and used like a compass to trace the shape of the base. Another rope is fastened to the ground on the inside base of the wall and used as a guide to shape the interior radius of the opposite wall of the dome. Ropes can be used from several points around the inside of the base to ensure accuracy of the finished dome. On top of each layer of tamped, filled tubes, a loop of barbed wire is placed to help stabilize the location of each consecutive layer. Window voids can be placed in two 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’ 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.
[edit] 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 concrete 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 Super Adobe 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.
[edit] 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 Super Adobe 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 Super Adobe 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 utilized with ease, Super Adobe 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 figure head said this about the emergency shelter aspects of Super Adobe: “A 400-square-foot 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.”
[edit] Sustainability
Super Adobe and other forms of Earth-Bag Construction are considered sustainable for several reasons. First of all, the system is extremely cheap and easy to build. Soil can be taken right from the site and the bags can be obtained for free or for a low cost. The technique demands few skills. Anyone can learn to do it, which makes this building technique accessible to low income communities. Additionally, the building can be erected very quickly, building with bags goes quicker then with any other Earth-building technique (i.e. Cob, Adobe, etc). Also, the system is very flexible, allowing for alterations in design and construction. This makes customizing a design to a specific individuals needs while the home is under construction relatively unencumbered compared to post permit alterations in modern day construction. Super Adobe is increasingly being realized as a Green building technique. Building sustainably does not just entail a focus on the health of the inhabitants of the structure or the environmental impacts of a certain technique or material. The ethics or social and economic impact of the technique and materials must also be considered. Sustainability implies a level of social awareness paramount to a healthy building culture. Super Adobe’s major ingredient is earth, which is non-toxic and readily available. If the earth is not from the immediate site than locating a nearby source is generally not terribly difficult, such close proximity to a materials source decreases the materials embodied energy, another focus of sustainability. In terms of energy conservation the walls are very thick and have significant thermal mass, which reduces heating and cooling costs as well as provides sound insulation, structural integrity, fire and pest protection. Like traditional adobe or concrete structures the walls are heated throughout the day, while maintaining a comfortable temperature on the inside. Then the heat is released slowly throughout night also contributing to a comfortable interior temperature. Another vital emphasis in green, or sustainable design is a structures connection to its natural environment. In the same interview with the AIA representative mentioned previously, Nader Khalili said this about his reason for creating the Super Adobe technique of construction. “I was searching for a way to create a building that was totally in harmony with nature, that could be available to everybody around the world.”
[edit] Properties
Super Adobe has also been proven to be competitively strong by modern western construction standards. Strength and resiliency tests done at Cal-Earth under the supervision of the ICBO (International Conference of Building Officials) showed that under static load testing conditions simulating seismic, wind, and snow loads, the Super Adobe system exceeded by 200 percent the 1991 Uniform Building Code Requirements. Due to this, California granted its first permit for the Earth Bag Construction for the Hesperia Museum and Nature Center. Earth bag shelters have since been built in the U.S., Mexico, Canada, the Bahamas, and Mongolia. Like many Sustainable building techniques, sand bag construction has gained interest in the public eye as environmental consciousness increases.
[edit] Criticisms
[edit] Structural design issues
Several building departments have required that substantial changes be made to designs to meet seismic building codes. Most building codes require positive vertical connections between structural members, but since Super Adobe is reinforced by barb wire placed between sand bag layers, no positive connection exists between bag layers to contain dynamic vertical loads and prevent separation. The Eco-Dome constructed at the Pomona College Organic Farm, in Los Angeles County, for example included a reinforcing rebar and welded wire mesh faced in shotcrete on both the inner and outer surfaces.
[edit] Architectural design issues
Some architects criticize Cal-Earth designs as being a 'regressive technique'. In a New York Times article11 Peter Berman, a Montana architect, raised objects over economy of scale. Berman asserts that technology should be foremost in architecture and that buildings should be 'lighter, stronger and more transparent'. Moreover, Berman has stated that he does not view Khalili as a professional, due in most part to his rejection of industrialized processes and products, stating the issues of installing "standard windows and doors".
[edit] High construction costs
As an experimental/developmental technique Super Adobe has been criticized as being overly-expensive, since the construction is so proportionally labor-intensive. Super Adobe, for this reason, is well suited for communal, volunteer constructions, or for places where the cost of labor is low. Within a commercial model, Mr. Khalili estimated that a four-bedroom, 2,000 square foot house would cost $75,000 to build, including labor, materials and utilities.
[edit] Poor insulation
The Cal-Earth Eco-Dome design has U-Factors of 0.103 (9.7 R-value) for 18 inch thick walls and 0.253 (3.9 R-value) for a 6 inch thick roof.
[edit] Use of energy intensive or petroleum-based materials
In the Super Adobe process, cement is mixed with earth in the ratio of 15 percent or more. A Cal-Earth design, such as the double Eco-Dome, requires 70,000 lbs of Portland cement for a structure having less than 800 interior square feet. Also, since earth contains materials such as clay or organic matter that interfere with the binding properties of cement, it may result in inefficient use of cement. In soils with high clay content Cal-Earth recommends increasing the percentage of cement or lime. Petroleum based materials, such as asphault emulsion are applied to the exterior surfaces of the structure for weatherproofing.
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[edit] Bibliography
- Khalili, Nader. "Nader Khalili." Cal-Earth. 19 Jan. 2007 [1].
- Katauskas, Ted. "Dirt-Cheap Houses from Elemental Materials." Architecture Week. Aug. 1998. 19 Jan. 2007 [2].
- Husain, Yasha. "Space-Friendly Architecture: Meet Nader Khalili." Space.com. 17 Nov. 2000. 19 Jan. 2007 [3].
- Sinclair, Cameron, and Kate Stohr. "Super Adobe." Design Like You Give a Damn. Ed. Diana Murphy, Adrian Crabbs, and Cory Reynolds. Ney York: Distributed Art Publishers, Inc., 2006. 104-13.
- Kellogg, Stuart, and James Quigg. "Good Earth." Daily Press. 18 Dec. 2005.
- Freedom Communications, Inc. 22 Jan. 2007 [4].
- Alternative Construction: Contemporary Natural Building Methods. Ed. Lynne Elizabeth and Cassandra Adams. New York: John Wiley & Sons, Inc., 2000.
- Hunter, Kaki, and Donald Kiffmeyer. Earthbag Building. Gabriola Island, BC: New Society Publishers, 2004.
- Kennedy, Joseph F. "Building With Earthbags." Natural Building Colloquium. NetWorks Productions. 14 Feb. 2007 [5].
- Aga Khan Development Network. "The Aga Khan Award for Architecture 2004." Sandbag Shelter Prototypes, various locations. 14 Feb. 2007 [6].
- The Green Building Program. "Earth Construction." Sustainable Building Sourcebook. 2006. 14 Feb. 2007 [7].
- NBRC. "NBRC Misc. Photos." NBRC: Other Super Adobe Buildings. 10 Dec. 1997. 14 Feb. 2007 [8].
- CCD. "CS05__Cal-Earth SuperAdobe." Combating Crisis with Design. 20 Sept. 2006. 14 Feb. 2007 [9].
- American Institute of Architects. A Conversation with Nader Khalili. 2004. 14 Feb. 2007 [10].
- New York Times. When Shelter is made from the Earth's Own Dust. 15 Apr 1999 [11]
