Earthbag construction is an inexpensive method to create structures which are both strong and can be quickly built. It is a natural building technique that evolved from historic military bunker construction techniques and temporary flood-control dike building methods. The technique requires very basic construction materials: sturdy sacks, filled with inorganic material usually available on site (such as sand, gravel, clay or crushed volcanic rock). Walls are gradually built up by laying the bags in courses — forming a staggered pattern similar to bricklaying. The walls are almost always curved to provide improved lateral stability, forming round rooms and domed ceilings like an igloo. To improve rigidity between each row of bags barbed wire is often placed between the courses. Twine is also sometimes wrapped around the bags to tie one course to the next, serving to hold the in-progress structure together and add strength. The structure is typically finished with plaster, stucco or adobe both to shed water and to prevent any degradation from solar radiation. This construction technique can be used for emergency shelters, temporary or permanent housing, barn or most conceivable small-to-medium-sized structures.
While architect and builder Nader Khalili popularized the methods and architecture of earthbag construction (particularly for residential buildings), it was the German professor of earthen architecture, Gernot Minke, who first developed a technique of using bags filled with pumice to build walls. Nader Khalili called his technique Superadobe, because he filled the bags with moistened adobe soil. Many examples of his work can be seen at the Cal-Earth Institute in Hesperia, CA, which he established in 1986 to popularize his ideas about natural construction techniques. Several books and videos have been produced by the institute to demonstrate his methods, however a number of other individuals and groups now offer training workshops. Khalili died at the age of 72 in 2008.
The basic construction method begins by digging a trench down to undisturbed mineral subsoil. Rows of woven bags (or tubes) are filled with available material, placed into this trench, and form a foundation. After the foundation is laid, each successive layer will have one or more strands of barbed wire placed on top. This digs into the bag's weave and prevents slippage of subsequent layers, and also resists any tendency for the outward expansion of walls (especially with domes). The next row of bags is offset by half a bag's width to form a staggered pattern. These are either pre-filled with material and hoisted up, or filled in place (often the case with Superadobe). The weight of this earth-filled bag pushes down on the barbed wire strands, locking the bag in place on the row below. The same process continues layer upon layer, forming walls. A roof can be formed by gradually sloping the walls inward to construct a dome. Traditional types of roof can also be made.
The most popular type of bag is made of woven polypropylene, such as the type often used to transport rice or other grains. Indeed, used grain bags are often reused as earthbags. Polypropylene is chosen for its low cost and its resistance to water damage, rot, and insects. Organic/natural materials such as hemp, burlap or other natural-fiber bags (like "gunny sacks") can be used; however, these may rot if not kept perfectly dry.
Generally inorganic material is used as filler, but some organic material (such as rice hulls) can also be used. Thermal insulating properties are an important consideration, particularly 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. On the other hand, thermal mass properties of the fill material are also an important consideration, particularly for climates that experience temperature extremes. Materials like clay or sand have excellent heat retention characteristics and, when properly insulated from the home's exterior, make a logical choice for incorporating a passive solar building design. Such a design has the capability of keeping a home's internal temperature stable year-round.
Forming the HouseEdit
Various types of roofs may be used, including earthbag extensions of the wall which create barrel vaulted or domed roofs, although vaulted roofs of much size are difficult to achieve with earthbags. Windows and doors are typically formed in with corbeling or brick-arch techniques, usually on temporary forms, or with a lintel supporting the top. Light may also be brought in by skylights, glass-capped pipes, or bottles which are placed between the rows of bags during construction. The addition of lintels will allow square windows to be used.
To prevent damage to the bags from UV rays or moisture, it is necessary to cover the exposed outer surfaces of the bags with an opaque material. There are many possibilities of what material to use, including stucco, plaster or adobe. This will usually also meet any waterproofing requirements, but such requirements can also be met by using additives in the bag-fill material. 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.
It's easy to posit that earthbag construction uses the least energy of any durable construction method. Unlike concrete, brick or wood, no energy is needed to produce the necessary materials other than gathering soil. With on-site soil being used, practically no energy is expended on transportation. And unlike rammed-earth construction, no energy is required to compact the soil. 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. The buildings last a long time; however, when they are no longer useful they may simply erode with no serious threat to the environment, or even be recycled into new earthbag-constructed buildings.
Colonization of the MoonEdit
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.
- EarthbagBuilding.com - Sharing information and promoting earthbag building.
- OKOKOK Productions - Site of veteran Earthbag builders, Kaki Hunter and Donald Kliffmeyer, also authors of an excellent how-to manual, Earthbag Building: the Tools, Tricks, and Techniques.
- Geiger Research Institute of Sustainable Building - Promoting natural building, and sustainable design and development, through research, training, education and consulting services.
- Cal-Earth - The California Institute of Earth Art and Architecture has developed a patented system called Superadobe, in which bags filled with stabilized earth are layered with strands of barbed wire to form a structure strong enough to withstand earthquakes, fire and flood.
- Earth Hands and Houses building with earthbag in Poland
- ArcheEarth Design
- Beehive Home Building Course offered by Broken Earth