One of the greatest needs in the world is disaster-resistant housing – houses that can hold up against hurricanes, earthquakes, fires, flooding and other natural disasters. Events like this that affect many of thousands of people seem to occur almost daily. It’s sad and painful to see so many lives lost, and so many families and homes upended. But it’s even sadder and more painful when you know most of this tragedy is preventable by using sound construction methods. Properly designed structures that can withstand natural disasters can save millions of lives and millions of structures every year.
Let’s start with challenge of rebuilding after the 2004 Asian tsunami. What methods and materials would work best to rebuild the region? Ideally, the houses would be very low cost, simple to build, require few special tools or skills and be incredibly strong – preferably as strong as bunkers used by the military, but yet still meet the typical needs of families around the world. Most options are too expensive, non-sustainable, impractical or culturally inappropriate. At or near the top of the list is earthbag construction.
For those who don’t know, earthbag buildings are made out of sand bags that are filled and stacked like masonry. Sand bags are also called earthbags, because they can be filled with any number of materials, including soil. They have a long history of use by the military for constructing bullet and blast resistant structures. Militaries around the world have used sand bags since the Napoleonic Wars about 250 years ago. That’s a very long record of proven performance, and sand bags are still used today because they have many desirable properties. The first sand bags were made of burlap; today they’re made out of woven polypropylene for even greater strength and durability.
Sand bags (or earthbags) also have been used for many years in flood control. Millions of bags are placed around communities every year to protect against flooding. Average citizens often pitch in and work together with no training to construct barrier walls to prevent flooding.
The same characteristics that make earthbags ideal for military and flood control use – strength, durability, simplicity of use, low cost – also apply to constructing houses. In addition, earthbag houses are fire resistant, non-toxic, do not attract pests and can be built to suit any climate. For instance, bags can be filled with insulation in cold climates.
It’s important to note that structural details can be changed to meet specific design requirements. For instance, lower walls can be filled with gravel in flood prone areas, and reinforced to resist lateral forces of flowing water. Instead of being swept away like typical wood-framed houses, families can return to their homes after a flood, clean the house and resume their daily lives.
Earthbag houses are also hurricane and tornado resistant. It’s best to use round and polygonal shapes such as hexagons and octagons when building in high wind areas. You want the wind to blow around the house instead of creating large flat surfaces where wind pressure can build up. Conical shaped roofs with minimal roof overhangs and sufficient roof tie-downs are recommended.
Earthbag buildings are also earthquake resistant. The key here is working closely with engineers to develop safe designs. This is done on a case-by-case basis, taking into account local soil properties and the degree of seismic risk. Engineered plans are now available for building with earthbags in seismic areas. Precision Structural Engineering, Inc. now offers code approved earthbag plans for seismic and non-seismic regions. In addition, our website at EarthbagStructures.com provides lots of drawings and easy to understand, low cost solutions for reinforcing earthbag houses against earthquakes and other natural disasters.
More testing is called for to fully document the strength of earthbag structures, but so far the results are very promising. Bryce Daigle’s testing and thesis, for example, details how earthbag walls obtain maximum compressive strengths almost 10 times as great as those typically achieved by conventional stud-frame housing in terms of load per meter of wall length. Testing Proves Earthbags Very Strong
Nadir Khalili’s tests in Hesperia, California demonstrated how earthbag structures exceeded the strength of the testing equipment with no deflection or failure, and received code approval in the most dangerous level — seismic zone 4. Gaining building code approval in California, the strictest area in the world as far as building codes, speaks volumes to the inherent strength of earthbags.
In addition to providing flood protection, gravel-filled earthbag foundations are being used by PAKSBAB, an NGO in Pakistan, because they are very strong in earthquakes. They conducted a shake table test at the University of Nevada, Reno, to simulate the devastating Northridge (Canoga Park) quake that occurred in California. According to their report, “the house survived 0.82g, twice the acceleration of the Canoga Park record. Although severely damaged, the building did not appear in danger of collapse, even at the end of the test sequence.”
Based on the successful completion of these tests, and lessons learned from thousands of earthbag structures around the world, about a dozen groups have chosen to build with earthbags in Haiti – a country with high risk of earthquakes, floods and hurricanes.
Some may wonder how this compares to building with concrete. The problem with concrete, other than being unsustainable because it’s a major contributor to global climate change, is excessive cost and difficulty in maintaining quality control. Properly built reinforced concrete structures, which can be engineered to high earthquake-resistance, are not affordable in Haiti and countless other areas around the world. So even with building codes and strong concrete designs, builders in these areas will typically find a way to circumvent codes and/or misappropriate valuable building materials. When a sack of cement costs upwards of a week’s wages, the temptation is just too great.
The need for disaster-resistant housing is a growing concern as more and more people now live in areas that are vulnerable to hurricanes, earthquakes, fires and other disasters. The high population density makes any disaster that much more deadly.
Also, destruction of natural habitat is exacerbating the problems as we can see with New Orleans and other areas along the Gulf coast. The trees that once provided a buffer against storms are now largely gone, and so wind and waves from hurricanes cause much more damage. This makes the need for disaster resistant structures that much more important.
And, there are enormous economic implications. It’s nearly impossible to build a thriving economy when year after year large sectors of a country are destroyed. We need the political and social will to move forward on this vital issue. Now is the time to address these challenges head-on.
More information is available at:Earthbag Testing page
Post-tsunami Affordable Housing Project
Emergency Earthbag Shelter Proposal