Earthbag construction harnesses the techniques used in military bunkers and for temporary flood control to create housing which requires little more than bags, barbed wire and a few tools. The rest of the material comes from the earth found in the surrounding region, significantly reducing the energy requirements of construction and the costs involved.
Earthen construction is nothing new, with humans having utilized the earth beneath their feet to create homes for thousands of years. But in recent years, a few modern-day materials have been applied to this ancient building technique, creating a sturdy and durable construction method. It not only addresses affordable housing needs in the developing world and disaster-hit regions, but also issues surrounding environmental degradation.
What is earthbag construction?
Earthbag construction usually begins with the digging of a trench down to the mineral subsoil which is then partially filled with gravel to create a foundation. Woven bags filled with gravel or adobe are then placed into the trench with strands of barbed wire placed in between each layer to prevent slippage and resist an outward expansion of the walls. Each successive layer of filled bags is offset by a half bag’s width to form a staggered pattern. These push down on the barbed wire to essentially “lock” the bags in place.
Solid-weave polypropylene bags are the most popular due to their water damage-, rot- and insect resistance, although hemp, burlap and other natural fibers can be used, provided they are filled with a high-percentage clay material. Clay helps the bags mold tightly around the barbed wire, improving the tensile strength of the walls. Sand, stone dust and gravel are able to survive prolonged soaking or flood conditions better but may need special bracing during construction.
The thermal insulating properties of the fill material should also be taken into consideration, particularly if built in climates which experience extremes of temperature. Both clay and sand have good heat retention characteristics and are popular choices for passive solar design in cool climate destinations, keeping the internal temperature relatively stable throughout the year.
After the walls are constructed, a roof can then be formed by gradually sloping the walls inward to create a dome or barrel-vaulted structure. A traditional roof can also be added on top of the walls or some opt for a green “living roof”. Windows and doors can be created using masonry lintel or brick-arch techniques, with skylights added during construction by placing bottles between the rows of bags. An exposed outer surface needs to be added to the earthbag construction to prevent damage from moisture or UV rays and cement-based stucco, lime or earthen plasters are among the most popular.
Who invented earthbag construction?
The German professor Gernot Minke is credited with being the first to fill bags with pumice in the construction of sturdy walls, but it was architect Nader Khalili from the Cal Earth Institute in Hesperia, California who really brought the idea to popular attention. He sought to find affordable housing solutions that tackled environmental degradation, coming up with the idea of “sandbag architecture” which drew on the earthen architecture found in his homeland, Iran. The institute in California was created to showcase his ideas for natural construction techniques and his work has been influential in gaining approval for the construction of earthbag domes in high seismic risk regions.
Advantages of earthbag construction
One of the main advantages of earthbag construction is the minimal energy requirements, with earth readily available in most regions and having the favorable qualities of being a termite-, rot- and fire-proof material. While energy is required to produce the bags and barbed wire, as well as the outer shell, these are used in relatively small quantities. Because earthbag structures are made from predominantly natural materials, they can also erode with no serious threat to the environment if they are no longer required. Earthbag construction is particularly advantageous in regions that have limited trees as it eliminates the need for wood resources in the walls and roof.
The tensile strength of earthbags is also of note, particularly when the bags are combined with four-point barbed wire which serves the same function as reinforcing rods used in rammed earth and concrete structures. While earth construction in humid regions normally requires some amount of cement, lime or asphalt emulsion to ensure the final material is resistant to water absorption, the bags used in earthbag construction provide mechanical stabilization and support the structure even when saturated. This means that a broader range of soil options are available to builders across humid regions, such as the Caribbean and Pacific Islands.
The durability of earthbag constructions have been tested under significant seismic, wind and snow conditions at the California Institute of Earth Art and Architecture and have passed all building code requirements. They have also been shown to withstand magnitude 6 and 7 earthquakes, together with floods, hurricanes and fires, and it’s this durability that makes them such a practical alternative to conventional building methods.
Disadvantages of earthbag construction
While the material costs of earthbag construction are relatively inexpensive, the method itself is quite labor-intensive. Most who choose to build this way do it themselves and the simplicity of the technique makes this easy to achieve or replicate in developing countries with the help of local community members.
Getting building permits for an earthbag house can also be trickier than a conventional structure and it may take perseverance on the part of the owner and coordination with local officials. Referencing similar projects that have received approval in your country is a good tactic for improving the chances of approval.
Earthbag construction in disaster relief housing
Earthbag construction has proved to be a practical solution to disaster relief and emergency shelters, as well as housing and institutional structures in the developing world. Following the 2004 tsunami which rocked Asia, earthbag construction techniques were tested in Sri Lanka, and they were also utilized for disaster relief housing following the earthquake which struck in Haiti in 2010. A number of earthbag homes had been built in Nepal prior to the devastating earthquake of 2015 and after surviving the impact, local builders have embraced the technique.
Nader Khalili has proposed that the construction method would be the most practical for building structures on other planets or the moon, with only lightweight bags and a few tools needed to be taken into space. While it may be early days for earthbag construction, it appears that the sky is the limit!