GREEN BUILDING BY SUPERADOBE TECHNOLOGY
Seminar Report 2012
Submitted by
Harishma Raveendran
ABSTRACT
Superadobe is a patented system at the service of humanity. Superadobe buildings use the structural principles of single and double curvature compression shells that have made arches, domes and also rectangular shapes. Individuals are enabled to build their own homes without the use of heavy equipment, with materials native to the country of use. Flood control, erosion control, stabilization of waters’ edges, hillside slopes and embankments, landscapes and infrastructures are applications in which superadobe system has shown great potential.
CONTENTS
1. INTRODUCTION 1
1.1 History 1
2. NEW APPROACH TO SAND BAGS 1
3. METHODOLOGY 3
3.1 Materials 3
3.2 Process 5
3.3 Finishing 6
4. STEPS OF CONSTRUCTION 7
5. STRUCTURAL CONSIDERATIONS 12
6. THERMAL PERFORMANCE 14
7. EMERGENCY SHELTERS 14
8. SERVICEABILITY CONSIDERATIONS 15
9. ADVANTAGES OF SUPERADOBE CONSTRUCTION 15
10. DISADVANTAGES 16
11. UNIVERSAL APPLICATION 17
12. CONCLUSION 17
REFERENCE 18
LIST OF FIGURES
1. Figure 1: UN Refugee camp 3
2. Figure 2 : Barbed weir 3
3. Figure 3 : compass 5
4. Figure 4 : Superadobe model 7
5. Figure 5 : Plastic pipe between tube layers for vents 7
6. Figure 6: Steps of construction 9
7. Figure 7: Double curvature compression shell 13
8. Figure 8 : Inside portion of a dome 13
9. Figure 9: Earthquake resistance 15
10.Figure 10: Fireproof resistance 16
1. INTRODUCTION
Approximately one third of the people of the world live in houses built with earth, and tens of thousands of towns and villages have been raised practically from the ground they are standing on. Today, world consciousness about the use of natural resources and the new perception of building codes as the steward not only of individual’s safety, but of the planet’s equilibrium, are leading us into the new millennium of sustainable living.
A Superadobe structure is made by filling long or short sandbags with earth from the building site and stacking or coiling them in to layers with barbed wares in between to serve as mortar and reinforcement. Bags and wire alone are adequate for short term use, such as in disaster relief; for a permanent home, cement or lime is added to the earth, the walls are coated with plaster, and the exterior gets a waterproof coating. Many Superadobe buildings use the structural principles of single and double curvature compression shells that have made arches and domes last for centuries, but Superadobe can also form rectangular shapes.
1.1 History
The technique’s current pioneer is Nader Khalili who originally developed the Superadobe system in 1984 in response to NASA call for housing designs for future human settlements on the Moons & Mars. His proposal was to use moon dust to fill the plastic Superadobe tubes and Velcro together the layers. In 1995 fifteen refugee shelters were built in Iran, Nader Khalili and the Uniteted 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 thousands. The government dismantled the camp a few years later. Since then, 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.
2. NEW APPROACH TO SANDBAGS
Common sandbags and connecting barbed wire, as well as mile-long bags, are referred to as Superadobe construction. For centuries, sandbags have been used as elements in building temporary dikes and protective walls in combat zones, as well as in numerous lesser applications. After the structure has served its temporary purpose, the sandbags normally are removed, emptied and discarded. Superadobe building system builds on three fundamental aspects of historical sandbag modules, resulting in a permanent system of construction:
The most serious drawback in the past concerning sandbags as a structural element is that a stack of bags has no tensile capabilities, which has kept structures very low in height. Also, curved, arched or domed structures were impossible without some friction and tensile resistance available.
Superadobe uses four-point barbed wire (or a similar element) between sandbag layers, allowing one to develop the tensile and shear capabilities that have not been previously achievable. The barbed wire element increases the friction factor between the bags and creates tensile resistance in a wall or structural element. It is an important aspect of Superadobe to provide for the transfer of shear stresses from one sandbag to another by using the barbed wire as an interface between the bags, overcoming problems of low shear capability in the earthen fill. The increased capacity of the sandbags, achieved by using barbed wire, creates the capability of designing higher walls and curved surfaces, such as bearing walls, arches, domes and vaults.
Previously, sandbags were not considered part of a permanent structure due to the use of loose fill material, usually sand, which can be loaded easily and discarded when the temporary structure is no longer needed.
Superadobe fabric tube or individual sandbags are packed with different mixes of fluent, particulate material. These include earthen, cementitious, organic, manufactured and recycled materials that form into a permanent block.
Historically, the potential deterioration of the bag and the subsequent effect on the structure has precluded permanent structures. Superadobe construction shields the sandbag walls from the elements with protective overlay materials. Additionally, the fill material becomes self-supporting once it has been formed into a block by the tubing. When the fill material is sufficiently resistant by itself, the shielding of durable exteriors is not necessary.
The Superadobe system, which has developed out of these fundamental changes during intensive research in the last seven years, is used in conventional structures for foundations (poured within the tubing form), for load-bearing and partition walls in conjunction with conventional roofing systems that bear on a bond beam, also generated by the Superadobe tube itself.
Figure 1: UN Refugee camp
Figure 2: Barbed weir
3. METHODOLOGY
3.1 Materials
The essential material in building with bags is, of course, the bags themselves. Most commonly the bags used are made of polypropylene or burlap. Polypropylene sacks come in a variety of sizes, and are extremely common. It is important that UV resistant bags be used, as deterioration by sunlight is the biggest danger. Recycled seed or feed sacks of polypropylene are often available for free from various sources. The sacks come in a variety of sizes and also come in a tube form, which is much cheaper to buy per square foot. Burlap sacks have also been used, but are not as durable and can also be more expensive, although they are a "natural" material. Custom-sewn bags have been created for special shapes, and "site sewn" custom bags can easily be made using bent nails or wire
The other essential material is that which fills the bag. A number of materials have been used, including sand, clay and gravel. While an ideal mixture would be a standard adobe mix of sand and clay, pretty much whatever subsoil is available is what has been used. The fill material can be used either wet or dry, but moistened material creates a more stable structure. An efficient system is to create your sack foundation and/or walls using soil from site excavation.
The most important consideration for bag choice is the material used to fill it. A good rule of thumb is the weaker the fill material, the stronger the bag material must be. In some cases, once a strong fill material has set, the bags could be removed from the exposed areas of the structure without any structural loss of integrity. On the other hand, if a weak material such as dry sand is used, it is essential that the bags be kept integral, and plastered as soon as possible.
Additional materials used in construction include barbed wire, used to keep the bags from slipping, and regular wire, which can be used to weave the bags similar to basket-making techniques. For extremely strong structures, cement can be used to create soil-cement mixtures to fill the bags. Old nails are often used to pin bags closed, create new shapes, and keep barbed wire in place.
Tools adapted to or developed for this technique are easily available or constructed. A wheelbarrow is used to transport materials and can be used to directly pour soil into larger bags. Stands to hold bags open for filling have been made with a variety of materials. Tube sections of cardboard or PVC, which fit into the longer tube-shaped bags, make filling these bags much easier. Mechanical pumps have been used at Cal Earth with great efficiency to fill the tubular bags. A tamper is an essential tool used to compact the bags once they are in place. The best tamper I have used was created from a 5 foot long 1 1/4" piece of metal pipe welded to a 6x6 1/4" metal plate. Coffee cans filled with soil can be tossed easily and used to fill bags higher up on the wall.
Simple forms of wood or metal are used with earth bags to create vaults, while domes are most effectively formed using a simple compass which acts as a placement guide for the bags. An excellent design for such a compass is to attach one end of a lightweight pipe (electrical conduit or an extendable pole used in pool cleaning) to a caster from which the wheel has been removed. This allows for articulation and rotation, and the caster can be easily attached to a 4x4 piece of wood set in the ground at the center of the dome. On the other end of the pipe, an excellent guide is a piece of "L" shaped metal attached with a pipe clamp. In order to create level rows of bags, a small adjustable level is attached near the guide end of the pipe where a person placing the bags can easily see it. Special compasses to create catenary shaped domes have also been developed. In addition to these guides used to create curved forms, I have used portable metal guide frames which are strung with levelling string to create straight walls.
Figure 3: compass
4.2 Process
The foundation for the structure is formed by digging a 12” (approx. 30cm) deep circular trench with an 8’-14’ (approx. 2 to 4m) diameter. Material removed from the foundation area
can be saved to fill the bags, setting aside topsoil and organic materials.
The fill material is then prepared. Again, subsoil is used, with large rocks and sticks being removed. For small site walls, this soil can be used dry, but for structural purposes, the fill material should be moistened and left overnight. The material should be made wet enough to compact well. Experience and practice will soon lead to proper moisture levels. The first couple of rows are often filled with gravel to preclude wicking of water into the wall.
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 super adobe 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.
4.3 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 Super adobe buildings have even been covered by living grass, a kind ofGreen roofbut covering the entire structure. Any exterior treatment and building details would need to be adapted to a region’s specific climatic needs.
Figure 4: Superadobe model
Figure 5: Plastic pipe between tube layers for vents
5. STEPS OF CONSTRUCTION
1) Collect the tools
2) Prepare the earth mix which is stabilized with cement or lime, or asphalt emulsion.