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
History
1 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
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2. Figure 2 : Barbed weir
3
3. Figure 3 : compass
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4. Figure 4 : Superadobe model
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5. Figure 5 : Plastic pipe between tube layers for vents
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6. Figure 6: Steps of construction
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7. Figure 7: Double curvature compression shell
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8. Figure 8 : Inside portion of a dome
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9. Figure 9: Earthquake resistance
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10.Figure 10: Fireproof resistance
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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 selfsupporting 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 2: 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. 30 cm) 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 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.
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. 3) Add enough water to ball together when squeezed, yet not leave the hand wet. If no cement or lime is available, use raw earth for a temporary shelter. (Experimental - try snow in bags and compact.) 4) Place the door away from wind and water. 5) Dig the foundation trench 30 cm (12”) deep. 6) Level and compact. (The foundation will be 2-3 completed bag rows.) 7) Place the bag in the trench, fold the end under to close, and start filling upright like a short column.
8) Always put in 2-3 cans of earth and shake to the end. 9) Use gravity's help by sloping the bag on your leg and walking backwards as it fills - do not strain. Let the bag fill as full as possible and check the position with the compass tool. 10) Twist and tuck under the bag ends to close. 11) Compact the filled bag as hard as you can using a tamper, to make a smooth, solid, uniform block. Only compacted earth becomes strong. 12) Attach continuous barbed wire - 1 wire for domes up to 4m (12 ft), 2 wires for bigger. Where breaks occur, overlap the wires by 2ft. (65 cm). 13) Continue coiling bags. 14, 15) Use compass to make the dome shape 16) Pre-cut bags for a doorway knock-out Panel. Stabilized earth must be cut after tamping at every row 17) Punch out pre-cut panels to open after a min. of 5 rows, or when the dome is completed 18) Insert pipes for windows sloped to outside for rain 19) Coil upper rows, but don’t stand on the wet bag 20) Fill and place bag above the row below and work it inwards to meet the compass circle. Tamp the bag with gentle slope to outside 21) Add an arched entry to the opening to buttress and protect the entrance 22) Plaster the exterior before bags disintegrate and 23) Waterproof with locally suitable materials to resist moisture and erosion 24) Finish with a water-resistant cement/lime plaster such as Reptile layered from bottom to top, or 25) A smooth cement or lime plasters finish
Fig 6.1: Step 1
Fig 6.2: Step 2 & 3
Fig 6.3: Step 4, 5 & 6
Fig 6.4: Step 7, 8 & 9
Fig 6.5 : Step 10
Fig 6.6: Step 11, 12 & 13
Fig 6.7: Step 14, 15, 16 & 17
Fig 6.8: Step 18
Fig 6.9: Step 21, 22 & 23
Fig 6.10: Step 24 Figure 6: Steps of construction
6. STRUCTURAL CONSIDERATIONS Superadobe techniques enable the construction of mono lithic structural systems built entirely from earth in curved forms. The sandbag, because of its flexibility, allows the construction of 9curved surfaces. When using single- and double-curvature compression shells ie arch, vault, dome etc the majority of conventional roofing systems can be eliminated. In the case of wood construction, this can save up to 95 percent of timber, allowing not only for forest products to be more wisely utilized but also resulting in fire-safe buildings. By working with the principle of gravity, these features can be built without special formwork. The success of the tested prototypes for California’s seismic codes and the resulting permits derive from the following principles:
Single- and double-curvature compression shells transfer their stresses along the surface of the structure and not from element to element like column- and beam-type buildings. When a single element in a beam and column construction is overloaded to failure, the loss of that element will create a cascading effect on adjacent elements, causing failure of all elements in the vicinity. In many cases, this will cause the entire structure to collapse, as was witnessed in earthquakes in Northridge, California, and Kobe, Japan. Such a structure is only as strong as its weakest element. In a dome, and to a lesser degree a vault, excessive loads on their surface will first cause a puncture failure. This results in the excessive load being shed with only localized damage; the remaining stresses in the vicinity of the failure are transmitted around the failed area, and other loads continue to be held by the structure without any problem.
Dead-load and live-load stresses are transferred to the supporting ground, spreading uniformly along the perimeter of a dome or bearing wall. In a beam and column structure, the loads are concentrated and transferred to the ground via a footing under each column. This situation creates the two basic structural problems of differential settlement and frost heaving. These can cause severe localized stresses within the upper structure, resulting in cracking and other failures. For this reason, most foundations are extended to below the frost line to minimize such problems. In a monolithic bearing wall, dome or vault, differential settlement and frost heaving do not pose severe problems. The base of a dome or bearing wall distributes the load of the structure over a much larger area, and local soft spots in the supporting soil will not
create a local problem, as local depressions may be easily spanned. The effect of frost can be rendered negligible with correct design when a dome is free to float on the ground.
One of the most significant advantages of a domed or vaulted bearing wall structure is its performance in earthquakes. It is difficult to design conventional structures to withstand earthquake stresses. Their basic shape creates a severe problem, as the building weight is either uniformly spread from roof to foundation or, even worse, weights are often larger in the upper floors. With this propensity for overturning, the deeply planted footings and foundations rip apart at the very base of the structure during an earthquake, causing failures rather than preventing them. Modern earthquake design that incorporates foundation isolation does have shifting capabilities, but it is expensive.
A dome or bearing wall built on a floating foundation, the base isolated by a layer of gravel or sand, provides the ideal earthquake-resistant structure. The continuous or ring foundation can slide across the moving ground, while the upper structure, which diminishes exponentially in mass toward the apex, performs as a unified monolithic piece, eliminating local failure higher up the building.
Figure 7: Double curvature compression shell
Figure 8: Inside portion of a dome
7. THERMAL PERFORMANCE Every material in a building has an insulation value that can be described as an R-value. Most builders think of R-value as a description of the ability of a structure or material to resist heat loss. This is a steady state value that doesn't change regardless of the outside temperature variations that occur naturally on a daily and annual basis. This R-value can also be expressed as the coefficient of heat transfer, or conductivity, or U-value, which is inversely proportional, that is U=1/R. From this simple formula we can see that material with a high Rvalue will yield a low U-value. U-value (units of thermal radiation) measures a material's ability to store and transfer heat, rather than resist its loss. Earthen walls function as an absorbent mass that is able to store warmth and re-radiate it back into the living space as the mass cools. This temperature fluctuation is known as the “thermal flywheel effect.” The effect of the flywheel is a 12-hour delay in energy transfer from exterior to interior. This means that at the hottest time of the day the inside of an earth bag structure is at its coolest, while at the coolest time of the day the interior is at its warmest. Of course this thermal performance is regulated by many factors including the placement and condition of windows and doors, climatic zone, wall colour, wall orientation, and particularly wall thickness. This twelve-hour delay is only possible in walls greater than 12 inches (30 cm) thick.
8. EMERGENCY SHELTERS According to Khalili's website, in 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. Labour 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. 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 figurehead said this about the emergency shelter aspects of Super
adobe: “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.”
9. SERVICEABILITY CONSIDERATIONS The floor of a Superadobe building is usually finished last so that plumbing and electrical lines can be run underneath to feed branches that extend upward where needed. Plumbing pipes are placed on, in, or under the lower Superadobe layers and run vertically through small channels cut in to the walls. Electrical lines are run through flexible conduit that follows the contours of the bags.
10. ADVANTAGES OF SUPERADOBE BUILDINGS
10.1 Earthquake safe Superadobe structure is safe against earthquake
Figure 9: Earthquake resistance
10.2 Fire proof During some of fire storms where hundreds of homes were destroyed due to combustible materials used in the building envelope. The only way to resist being burned is to be “non flammable”, earth is such a material.
Figure 10 : Fireproof resistance 10.3 Wind proof Wind is a very powerful force that travels in a path it chooses. As wind travels it tends to build force and get stronger and more powerful and relentless. A superadobe dome and vault shape for use as homes or shelter has much to offer when it comes to wind forces.
10.4 User friendly The technology and form is easy to understand and follow. Our brain is not overwhelmed by the idea of shelter. When people look at the dome and vault structure because of the “simplicity” can embrace it without getting lost in the concept of how it was built. The application and erection of new homes will be welcome in any region or country it is placed. It will provide many people with new jobs and give them the ability to be involved building something permanent and needed using the “greenest of the green technologies available today”.
10.5 Easy to learn Those involved in learning how to build with it, will be very happy knowing that they can build a home for others made of earth and that the building they are building will be there for generations to come.
11. DISADVANTAGES
It does take a lot of people to build a house by hands only.
It gets difficult after several hours of lifting the heavy bags.
It isn’t easy to understand at first when you look at the way it is being built.
It takes strength to lift and carry each bucket.
It’s hard on your back, feet and hands
If you are not used to work physically you will be tired sooner.
12. UNIVERSAL APPLICATIONS Modern computer software now allows for structural design analysis on an individual basis. The computer will also permit the utilization of the Superadobe systems in space and planetary construction based on performance programs, such as finite element analysis. The construction of infrastructures, structures and shielding elements, such as for thermal, radiation and/or impact shielding on the moon and Mars, would otherwise imply costly transportation of building materials into outer space. The utilization of in-situ, minimally processed materials, is crucial to space exploration.
Flood control; erosion control; stabilization of waters' edges, hillside slopes and embankments; and retaining walls, landscapes, and infrastructures are applications in which the Sandbag/Superadobe/Superblock system has shown great potential.
Individuals are enabled once again to build their own homes without the use of heavy equipment, with materials native to the country of use. All the skills required are simple and can be acquired by anyone who wishes to learn them. The Superadobe system can use existing contractor’s machinery, such as concrete and gunnite pumps, to mechanize the packing of the fill material into the bag forms.
13. CONCLUSION Superadobe is an adobe that is stretched from history in the new century. It is like an umbilical cord connecting the traditional with the future adobe world. Individuals are enabled once again to build their own homes without the use of heavy equipment, with materials native to the country of use. Superadobe has been used internationally by UN for emergency housing prototypes and is currently in limited use on several continents and under construction in several places. While many challenges lie ahead, it is still a hopeful and exciting time to be part of this quest to create a sustainable human culture.
REFERENCE
Kennedy J, M. Smith, & C. Wanek , “Building with earth bags”, journal of the art of natural building, 2002, pp. 149-153
Brooke Barnes, Mihyun Kang, and Huantian Cao,“Design of sustainable relief housing in Ethiopia: an implementation of cradle to cradle design in earth bag construction”, Journal of Environmental Sciences, 2006, Vol 5, pp. 137
Ronald Rael (1971), Earth Architecture, first edition, Princeton Architectural Press
Paul G. Mc Henry(1989), Adobe and Rammed Earth Buildings: Design and Construction, The University of Arizona Press n
en.wikipedia.org/wiki/superadobe
calearth.org >Building designs
www.earthbagbuilding.com/articles.htm
Naturalbuildingblog.com/earthbagsuperadobe-house-construction-vid
