Earthbag construction

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Earthbag construction is an inexpensive building method using mostly local soil to create structures which are both strong and can be quickly built.

Contents

Earthbag development

Features

It is a natural building technique developed from historic military bunker construction techniques and temporary flood-control dike building methods. The technique requires very basic construction materials: sturdy sacks filled with organic material usually available on site.

Standard earthbag fill material has internal stability. Either moist subsoil that contains enough clay to become cohesive when tamped, or a water-resistant angular gravel or crushed volcanic rock is used. Walls are gradually built up by laying the bags in courses—forming a staggered pattern similar to bricklaying.

The walls can be curved or straight, domed with earth or topped with conventional roofs. Curved walls provide good lateral stability, forming round rooms and/or domed ceilings like an igloo.

Buildings with straight walls longer than 5 m (16.4 ft) in length need intersecting walls or bracing buttresses. International standards exist for bracing wall size and spacing for earthen construction in different types of seismic risk areas, most notably the performance-based standards of New Zealand [1] recommended by the ASTM International's earth building standards. [2] Static shear testing shows that earthbag can reach similar strengths to New Zealand's reinforced adobe standards with specific soil strengths and reinforcement [3] although unreinforced weak soil earthbag can have lower shear strength than unreinforced adobe.

To improve friction between bags and wall tensile strength barbed wire is usually placed between courses. Twine is also sometimes wrapped around the bags to tie one course to the next, to hold in-progress structures together and keep courses well-seated on barbed wire prongs. [4] Rebar can be hammered into walls to strengthen corners and opening edges and provide resistance against overturning.

The structure is typically finished with plaster, either cement stucco on a strong mesh layer or an adobe or lime plaster, to shed water and prevent fabric UV damage. Finishes can differ from protected interior applications to exposed external applications.

This construction technique is one of the most versatile natural building methods and can be used for benches, freestanding walls, emergency shelters, temporary or permanent housing, or barns and commercial buildings. Earthbag is frequently chosen for many small-to-medium-sized institutional structures in the developing world. Subgrade structures including underground and bermed dwellings (such as Earthships), cisterns, spring boxes, root cellars, and retaining walls can be built with stabilized soil fill or with additional reinforcement and water-resistant gravel or sand fill.

Writers

Although Joseph Kennedy probably invented the term earthbag (as well as contained earth), Paulina Wojciechowska wrote the first book on the topic of earthbag building in 2001, Building with Earth: A Guide to Flexible-Form Earthbag Construction. Kelly Hart developed a massive online database of earthbag information that encouraged idea sharing. Kaki Hunter and Doni Kiffmeyer worked on a variety of projects after studying with Khalili, calling earthbag "flexible form rammed earth". Their 2004 book, Earthbag Building: the Tools, Tricks and Techniques, is available as an e-book. [5]

Free online booklets have been developed by different authors, including Owen Geiger and Patti Stouter. These include structural research and field testing techniques developed for rural areas. [6]

A 2011 e-book by Geiger, Earthbag Building Guide: Vertical Walls Step-by-Step, provides photo illustrations of the process and discussions of new techniques for low-risk areas. [7]

Proponents

Many like Akio Inoue, from Tenri University in Japan and Scott Howard of Earthen Hand have tested and built buildings. Hart, with Geiger, [8] encouraged earthbag's development into different culturally and climatically-appropriate shapes. Robert Shear built an earthship inspired earthbag house in Utah and Morgan Caraway of Sustainable Life School is building a house that incorporates earthship design principles as well.

While Gernot Minke, the German professor of earthen architecture, first developed a technique of using bags filled with pumice to build walls, architect and builder Nader Khalili helped reintroduce earthbag construction as a modern technique called superadobe for humanitarian efforts (particularly for residential buildings) as well as natural flood control. [9]

Dr. John Anderton of South Africa has tested a triple channel bag version that reduces the slumping problems inherent in non-cohesive fill material like sand, [10] and pioneered work in a narrow wall contained sand system which he calls E-khaya.

Fernando Pacheco of Brazil pioneered the use of lighter HDPE mesh tubing for simpler hyperadobe walls. [11]

Rebuilding after natural disasters and in low-income regions around the world has included earthbag. Although heavy earthen walls are usually dangerous in quakes, Nepal's spring 2015 earthquakes left earthbag buildings in good condition near destroyed buildings.

Engineer Nabil Taha developed the first general specifications for one type of exterior pinning reinforcement appropriate for the highest seismic risk zones. [12] Several engineering students have tested uncured or low strength earthbag, and Build Simple has tested cured cohesive walls. [13] Organizations building in Nepal are currently working with engineers to improve and refine reinforcement options for seismic-resistant earthbag.

Construction method

Timelapse video of an earthbag building being made

Construction usually begins by digging a trench to undisturbed mineral subsoil, which is partially filled with stones and/or gravel to create a rubble trench foundation. In high seismic risk regions a reinforced concrete footing or grade beam may be recommended. Earthbag buildings can also be built on conventional concrete slabs (though this is more expensive and uses more embodied energy than a rubble trench foundation) and can have a bermed or underground "floating" foundation like an earthship as well.

Several courses of gravel in doubled woven bags form a water-resistant foundation. Each layer usually has two strands of barbed wire on top, that attaches to the bag to prevent slippage and resists any tendency for the outward expansion of dome or rectangular walls.

Bags on the course above are offset by 200 mm (8 in)—half of the 450 mm (18 in) wall width—similar to running bond in masonry. Bags can either be pre-filled with material and hoisted up, or bags or tubes are filled in place. The weight of the earthen fill locks the bag in place on the barbed wire below. A light tamping of the bags or tubes consolidates the moist clay-containing fill and creates interlocking bags or tubes anchored on the barbed wire.

Container types

Solid-weave polypropylene is most popular, available around the world to transport rice or other grains. Polypropylene is low cost and resists water damage, rot, and insects. Tubes are often available from manufacturers who sew them into bags. Mesh tubes of soft crocheted poly fibers are also used, although stiff extruded mesh or woven mesh bags can also be used.

Organic/natural materials such as hemp, burlap (like "gunny sacks") can be used. Since these may rot, they should only be used with cohesive fills (containing a significant proportion of clay) that form solid masses when tamped.

Terminology

Types of contained earth Types of Contained Earth.jpg
Types of contained earth

Earthbag is now a varied family of techniques. Each type of fill and container has different strength and reinforcement requirements.

For hazardous locations, accurate terminology is needed. Contained earth (CE) is based on the original technique, but with specific soil strengths and reinforcement chosen for hazard levels. CE uses damp, cohesive, tamped bag fill, which bonds strongly with barbed wire and other reinforcement as the wall cures.

CE is not "sandbags". Contained sand (CS) uses sand fill or any fill too dry or with poor cohesion that performs structurally like sandbags. CS must be built with solid-weave fabric bags and have good protection from fabric damage, relying on the strength of the bag fabric for wall strength. [14] CS needs more vertical reinforcement for both shear and out-of-plane strength than CE, or may require a structural skin. Some builders use narrow bags of contained sand as wall infill.

Contained gravel (CG) uses fill of any aggregate larger than coarse sand, usually in doubled rice bags, although strong mesh can be used. CG limits dampness transmission from footings.

Modular CE is built in grain bags or similar tubes. Walls rely on attachment between barbed wire barbs and/ or added pins between courses. Solid CE is hyperadobe built in some type of knit raschel mesh tube, so that the damp earthen fill solidifies between courses.

Bag-fill materials

Generally inorganic material is used as filler, but some organic material (such as rice hulls) can be used if a strong matrix like wire mesh reinforces the plaster.

Earthen fill may contain 5–50% clay, and can be "reject fines", "road base", "engineered fill", or local subsoil. "Raw" or un-stabilized soils cure as solid units but cannot withstand prolonged soaking. Subsoils with clay mold tightly and attach well to barbed wire prongs and rebar.

Soil fill can contain a high proportion of aggregate, as long as it tamps and cures strongly. Crushed bottles, strong rubble, or plastic trash can be used, but high aggregate mixes may interfere with inserting rebar.

Sands, stone dust and gravels can survive prolonged flood conditions, but most require special bracing during construction as well as some form of structural skin. Sand fill may be appropriate for several courses to provide a vibration damping building base, but becomes unstable in ordinary bags above 60–100 cm (24–39 in) in height.

Cement, lime or bitumen stabilization can allow clay soil to withstand flooding or allow sands to be used in traditional bags with a non-structural plaster skin. Because earthbag walls are usually 38 cm (15 in) thick a large amount of stabilizer is needed.

Thermal insulating properties are important for climates that experience temperature extremes. The thermal insulating value of a material is directly related to both the porosity of the material and the thickness of the wall. Crushed volcanic rock, pumice or rice hulls yield higher insulation value than clay or sand. Untreated organic materials that could decay should not be used as part of a structural wall, although they can be used as infill.

United Earth Builders has tried a light straw clay in the hyperadobe mesh tubing to form a layer 200 mm (8") thick outside of a dome. [15]

Thermal mass properties of earthen fill moderate temperature swings in climates that experience high temperature fluctuations from night to day. This thermal flywheel effect makes massive earth walls ideal for mild or hot and dry climates. Clay or sand also have excellent heat retention characteristics and, when properly insulated from the home's exterior, can serve as thermal mass in a passive solar building design in cool climates, keeping interior temperatures stable year-round.

Reinforcement and structural performance

Solid CE may be built with less barbed wire in low-risk areas because walls solidify between courses. Earthbag using woven bags or tubes need barbed wire for any level of natural hazard since the bag-to-bag surfaces are slippery. Pins between courses do not contribute important linear out-of-plane strength. [16] Walls of earthbag with barbed wire are more flexible than adobe and may resist collapse when carefully detailed.

Earthbag of weak soil with no steel can be half the shear strength of unreinforced adobe, which is easily damaged in earthquakes. New Zealand's code detailing and plans allow unreinforced adobe walls to survive almost 0.6 g forces (comparable to Ss values for 2% probability of excedance in 50 years), but earthbag needs stronger soil to match this strength. Earthbag in Nepal surpassed this strength slightly by resisting forces above 0.7 g in early 2015. [17] Domes tested in California resisted approximately 1 g forces, due to the stable shape of these less than 7 m (23 ft) diameter buildings. [18]

Current earthbag techniques of inserting rebar unattached to base and overlapping without connection may only resist 1.2 g or less, even if using very strong soil. Special reinforcement is needed

Solid CE of strong soil has higher shear and out of plane strength than modular CE,. [19] It may also allow the use of mesh for horizontal reinforcement in addition to or in place of barbed wire.

Contained gravel or contained sand may perform best with wire wrapped around the sides of straight wall sections, alternating with the next course having barbed wire gift-wrapped under and over the same straight sections. Base walls of CG in high risk regions may need additional buttresses at the foundation level where builders cannot afford a reinforced concrete (RC) grade beam or footing. A narrower plastic mesh tube often used for erosion control wattle could be filled with gravel to allow a half-width RC ring beam under the wide walls.

Forming the house

A roof can be formed by gradually sloping the walls inward to construct a dome. Vaulted roofs can be built on forms. Or a bond beam is used under a traditional roof type. Hip roofs, gable-type trusses or vigas may be needed to reduce outward stress on earthen walls.

Earth domes are inexpensive to build, but waterproofing them is complex or expensive in humid regions.

Windows and doors can be formed with a traditional masonry lintel or with corbeling or brick-arch techniques, on temporary forms. Light may also be brought in by skylights, glass-capped pipes, or bottles placed between bag courses during construction.

Finishing

Cover the wall to prevent damage to the bags from UV rays or moisture with cement-based stucco, or lime or earthen plaster. If walls are 'raw' earth, an infill plaster of earth with straw is used to fill the nooks between bags or courses. A finish plaster is applied on top.

Roof overhangs are helpful to reduce plaster waterproofing requirements, although plaster on lower walls may be stronger and more water-resistant than plaster on upper walls.

Some buildings use a planted-earth "living roof" ("green-roof") to top the structure, while others use a more conventional framing and roof placed atop earth-bag walls.

Environmental friendliness

Earthbag construction uses very little energy compared to other durable construction methods. Unlike concrete, brick or wood, no energy is needed to produce the earthen fill other than gathering soil. If on-site soil is used, little energy is needed for transportation. Unlike rammed earth construction, only human labor energy is required to tamp the soil lightly. The energy-intensive materials that are used – plastic (for bags & twine), steel wire, and perhaps the outer shell of plaster or stucco – are used in relatively small quantities compared to other types of construction, often totaling less than 5% of the building materials. Buildings last a long time when maintained. However, if "raw" or unstabilized soil is used as fill, when the building is no longer useful the earthen fill can be recycled into either garden areas, backfill, or new earthen buildings.[ citation needed ]

Use in disaster areas

Earthbag building techniques were also explored in Sri Lanka after the 2004 tsunami. [20] Multiple earthbag construction projects have been completed in Haiti, most of these after the earthquake. [21] First Steps Himalaya [22] and other charities had built more than 50 earthbag buildings in Nepal prior to the April 2015 earthquake. Since then, local builders flocked to ongoing earthbag training opportunities, including those by Good Earth Global, which have led to official Nepal building code acceptance of this technique for residences. International NPOs have built hundreds of contained earth or earthbag buildings in Nepal as well, more residences than larger clinics or schools. NPOs are asking for more structural information to be better able to choose reinforcement types and intensity appropriate to local soil strength and seismic risk. University testing has begun but more is needed.[ citation needed ]

Colonization of the Moon and Mars

Khalili proposed using the techniques of earthbag construction for building structures on the Moon or other planets. Currently, it is quite expensive to lift a positive-mass payload from Earth. Thus, Khalili's techniques would seem to be an ideal solution as the requisite supplies would consist of lightweight bags and a few tools to fill them. He specified that such bags would probably have pre-sewn "hook and loop" (i.e. Velcro) fastener strips in lieu of barbed wire.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Adobe</span> Building material of earth and organic materials

Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of earthen construction, or various architectural styles like Pueblo Revival or Territorial Revival. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials, and is used throughout the world.

<span class="mw-page-title-main">Masonry</span> Building of structures from individual units of stone, bricks, or blocks

Masonry is the craft of building a structure with brick, stone, or similar material, including mortar plastering which are often laid in, bound, and pasted together by mortar. The term masonry can also refer to the building units themselves.

<span class="mw-page-title-main">Mud</span> Mixture of water and any combination of soil, silt, sand, and clay

Mud is loam, silt or clay mixed with water. It is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone. When geological deposits of mud are formed in estuaries, the resultant layers are termed bay muds. Mud has also been used for centuries as a construction resource for mostly houses and also used as a binder.

<span class="mw-page-title-main">Cob (material)</span> Building material made of soil and fiber

Cob, cobb, or clom is a natural building material made from subsoil, water, fibrous organic material, and sometimes lime. The contents of subsoil vary, and if it does not contain the right mixture, it can be modified with sand or clay. Cob is fireproof, termite proof, resistant to seismic activity, and uses low-cost materials, although it is very labour intensive. It can be used to create artistic and sculptural forms, and its use has been revived in recent years by the natural building and sustainability movements.

<span class="mw-page-title-main">Building material</span> Material which is used for construction purposes

Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings and other structures, like bridges. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacturing of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, insulation, plumbing, and roofing work. They provide the make-up of habitats and structures including homes.

<span class="mw-page-title-main">Rammed earth</span> Construction material of damp subsoil

Rammed earth is a technique for constructing foundations, floors, and walls using compacted natural raw materials such as earth, chalk, lime, or gravel. It is an ancient method that has been revived recently as a sustainable building method.

<span class="mw-page-title-main">Retaining wall</span> Artificial wall used for supporting soil between two different elevations

Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to. They are used to bound soils between two different elevations often in areas of inconveniently steep terrain in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses. A retaining wall that retains soil on the backside and water on the frontside is called a seawall or a bulkhead.

<span class="mw-page-title-main">Stucco</span> Construction material made of aggregates, a binder, and water

Stucco or render is a construction material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as a decorative coating for walls and ceilings, exterior walls, and as a sculptural and artistic material in architecture. Stucco can be applied on construction materials such as metal, expanded metal lath, concrete, cinder block, or clay brick and adobe for decorative and structural purposes.

<span class="mw-page-title-main">Sandbag</span> Sturdy sack used in flood control and temporary military fortifications

A sandbag or dirtbag is a bag or sack made of hessian (burlap), polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification in trenches and bunkers, shielding glass windows in war zones, ballast, counterweight, and in other applications requiring mobile fortification, such as adding improvised additional protection to armored vehicles or tanks.

<span class="mw-page-title-main">Natural building</span> Sustainable construction practice

Natural building is the construction of buildings using systems and materials that emphasize sustainability. This in turn implies durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while recycled or salvaged, produce healthy living environments and maintain indoor air quality. Natural building tends to rely on human labor, more than technology. As Michael G. Smith observes, it depends on "local ecology, geology and climate; on the character of the particular building site, and on the needs and personalities of the builders and users."

<span class="mw-page-title-main">Ferrocement</span> System of reinforced mortar or plaster

Ferrocement or ferro-cement is a system of construction using reinforced mortar or plaster applied over an "armature" of metal mesh, woven, expanded metal, or metal-fibers, and closely spaced thin steel rods such as rebar. The metal commonly used is iron or some type of steel, and the mesh is made with wire with a diameter between 0.5 mm and 1 mm. The cement is typically a very rich mix of sand and cement in a 3:1 ratio; when used for making boards, no gravel is used, so that the material is not concrete.

Rice-hull bagwall construction is a system of building, with results aesthetically similar to the use of earthbag or cob construction. Woven polypropylene bags are tightly filled with raw rice-hulls, and these are stacked up, layer upon layer, with strands of four-pronged barbed wire between. A surrounding "cage" composed of mats of welded or woven steel mesh on both sides and then stuccoed, to form building walls.

Cast Earth is a proprietary natural building material developed since the mid-1990s by Harris Lowenhaupt and Michael Frerking based on the earlier Turkish Alker, which is a concrete-like composite with soil of a suitable composition as its bulk component stabilized with about 15% calcined gypsum instead of Portland cement. It can be used to form solid walls that need not be reinforced with a steel frame or timber framing, unless extra seismic reinforcement is necessary. Forms are set up and filled with Cast Earth, which sets quickly and solidly. Once the forms are removed the wall stays sound.

<span class="mw-page-title-main">Earth structure</span> Building or other structure made largely from soil

An earth structure is a building or other structure made largely from soil. Since soil is a widely available material, it has been used in construction since prehistoric times. It may be combined with other materials, compressed and/or baked to add strength.

<span class="mw-page-title-main">Compressed earth block</span> Building material

A compressed earth block (CEB), also known as a pressed earth block or a compressed soil block, is a building material made primarily from an appropriate mix of fairly dry inorganic subsoil, non-expansive clay, sand, and aggregate. Forming compressed earth blocks requires dampening, mechanically pressing at high pressure, and then drying the resulting material. If the blocks are stabilized with a chemical binder such as Portland cement they are called compressed stabilized earth block (CSEB) or stabilized earth block (SEB). Typically, around 3,000 psi (21 MPa) of pressure is applied in compression, and the original material volume is reduced by about half.

<span class="mw-page-title-main">Superadobe</span> Form of earthbag construction

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

Ceramic houses are buildings made of an earth mixture which is high in clay, and fired to become ceramic. The process of building and firing such houses was developed by Iranian architect Nader Khalili in the late 1970s; he named it Geltaftan. "Gel" means "clay" and "taftan" means "firing, baking, and weaving clay" in Persian language. Khalili's research into creating ceramic houses was strongly based on the idea that permanent, water-resistant, and earthquake-resistant houses could be built with the implementation of the four elements: earth and water to build the forms, and fire and air to finish them. His impassioned work led to a few small scale projects in Iran, including the Javadabad Elementary School, and the Ghaled Mofid restoration project. Aside from Khalili's own documented work, there seems to be little widespread research on ceramic houses.

<span class="mw-page-title-main">Cellular confinement</span> Confinement system used in construction and geotechnical engineering

Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention. Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete.

<span class="mw-page-title-main">Wattle and daub</span> Building technique using woven wooden supports packed with clay or mud

Wattle and daub is a composite building method used for making walls and buildings, in which a woven lattice of wooden strips called "wattle" is "daubed" with a sticky material usually made of some combination of wet soil, clay, sand, animal dung and straw. Wattle and daub has been used for at least 6,000 years and is still an important construction method in many parts of the world. Many historic buildings include wattle and daub construction.

<span class="mw-page-title-main">Contained earth</span> Earthbag construction material and method

Contained earth (CE) is a structurally designed natural building material that combines containment, inexpensive reinforcement, and strongly cohesive earthen walls. CE is earthbag construction that can be calibrated for several seismic risk levels based on building soil strength and plan standards for adequate bracing.

References

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