What is it?
According to some estimates, one-third of the world’s population is housed in earth buildings. Building in earth has a very long history, and has been practised in regions as diverse as Asia, Europe, Africa, the Americas, and in modern times Australia. The adobe buildings of the Southwestern United States are well known, as are the astonishing earth buildings, indeed earth cities, of Africa. Across Europe, earth has long been used in construction, either as infill, daub, or to build earthen walls like cob, or witchert in places like Buckinghamshire.
Earthbag building then, is a modern twist on perhaps humanity’s most important building tradition.
Bags or tubes are filled with earth (a suitable aggregate, sometimes with additions, and if you’re really lucky it’ll just be the stuff you moved to make the site for your building), and then placed in walls; barbed wire is used as a tie or ‘mortar’, and the bags are ‘rammed’. Most often then, the earth cures, and makes solid walls which no longer rely on the bags or tubes for their integrity.
From its origins in the building of military bunkers, and in flood defence, earthbag has been developed and applied around the world. It has been widely tested both structurally and thermally.
The history of earthbag building is covered in detail in a very readable article by Kelly Hart.
What are the benefits?
One of the reasons why earthbags were so widely used for military purposes and for flood defence is that the materials are easily transportable and easy to assemble. The advantages of the technique however are much more extensive than this. Kelly Hart’s colleague, Dr Owen Geiger put it this way:
‘Earthbag is extremely versatile and strong, and also very low-cost and simple. It’s ideal for harsh climates and regions with hurricanes and earthquakes. A large portion of humanity lives in hazardous areas like this and so earthbag building has enormous potential. Just look at Nepal for instance. All of the 50-some earthbag buildings survived the recent earthquakes with little or no damage even though they were not built to the highest standards.’
Cost-effective and community-empowering, earthbag buildings share their ‘feel’ with earth structures of other, older styles. Dr Geiger again:
‘The final homes feel wonderful – very safe and secure. You could literally drive a speeding truck into the side of these structures and cause only minor damage such as chipped plaster. Right now in Nepal, people want to stay in the earthbag buildings because they’re fearful of their concrete and brick houses. In hot climates like where I live, they stay cool and comfortable 24 hours a day every day of the year with appropriate design.’
I asked Dr Geiger about the durability of earthbag structures, and about any limitations he could see in the technique:
‘Earthbags evolved from use in the military and flood control. They are bomb, bullet and flood resistant if built correctly and therefore should have a very long lifespan. Just keep in mind that buildings made of earth and other high mass materials such as stone are not the best choice in cold climates. You could add exterior insulation, of course, but straw-bale seems like the best solution for Canada, northern US, etc.’
One of the most noticeable things about straw-bale building for example, and the same is true of cob, is that the relative simplicity of the method makes builders of people who have never thought of themselves as such. Dr Geiger puts it this way:
‘Each step can be demonstrated in a few seconds as you can see on my free YouTube videos. https://www.youtube.com/user/naturalhouses. I’ve taught housewives, 75-year-olds, teenagers, you name it – even those who speak no English. It boils down to filling buckets with moist soil, dumping it in bags and tamping them solid. It’s super simple. The only difficult part is standard carpentry. Every home needs doors, windows, etc. and that’s where it’s helpful to check out a carpentry book from the library with lots of good drawings.’
What can I do?
Wherever you have a suitable material to fill bags, you can build. Originally, for military bunkers and flood defence, burlap sacks were used, but modern earthbag builders mostly use woven polypropylene bags. The world is full of polypropylene bags, such an over-supply almost demands a use in construction. Tubes are also commonly employed, in a practice known as superadobe; and a material called Raschel mesh (which can be UV-protected) is sometimes used for the tubing – this is called hyperadobe!
Dr Geiger had to say to me on the matter:
‘Polypropylene bags and tubes are by far the most common material. Raschel mesh is gaining in popularity (hyperadobe). Poly bags are extremely strong and, according to the US Dept. of Transportation, will last at least 500 years if kept out of sunlight. That’s the main weakness – poly bags and Raschel mesh bags break down in UV, so we always emphasize the importance of protecting the bags until the walls are plastered.’
As for the material to fill the sacks, if the earth is going to provide the strength in the wall system as it cures, then earthbag builders need a soil that is approximately 30% clay and 70% sand. This is the standard soil for rammed earth building, what Hunter and Kiffmeyer call ‘the Ultimate Clay/Sand Ratio’. Earthbag can be used where clay is not present in these quantities by importing materials to the site, or by relying more on the integrity of the bags or tubes in the design. Under these circumstances, earthbag infill systems can also be considered, that is to say, much like straw bales, earthbag can be combined with a timber frame of some sort.
Dr Geiger pointed out to me that earthbag is not necessarily the best material in cold climates like Canada for example, and that straw-bale has advantages where super insulation is required. Nonetheless, earthbags can be made more insulating through the addition of materials like rice hulls, or hemp perhaps, and earth-sheltering can make earthbag building feasible even in regions with very cold winters. Hunter and Kiffmeyer remind us that ‘the earth itself is nature’s most reliable temperature regulator’.
Earthbag structures can be finished in a range of ways, but cement is often used on the exteriors, with earth plasters on the interior. This is what Dr Geiger had to say about the use of cement (not the ecological builder’s ideal material):
‘Most people use cement plaster because that’s what’s most available. For instance, lime is not available where I live. I’d have to buy a whole truckload from 600 miles away. And local plasterers don’t know how to use it. Plus, cement plaster is harder and will withstand hard driving rains.’
Lime plasters can also be used of course, applied by hand, trowel, or spray gun, and certainly would not bring the recognised environmental impacts of cement, including its contribution to CO2 emissions worldwide.
Polypropylene is susceptible to UV damage, so walls should be protected from exposure to the sun before they are rendered (builders’ sheets hung over or down the walls would do the job). As noted above, Raschel mesh can be UV-protected. Old fashioned burlap sacks are not UV sensitive, but they do wick moisture, so whilst it would be possible to build with burlap, such buildings would no doubt need the ‘good hat and stout pair of boots’ demanded of cob or straw-bale structures.
Earthbag building has given rise to a distinctive dome style of construction, with arched windows and doors, and very many round buildings. This aesthetic has arisen because earthbag building, particularly superadobe, is well suited to such expression, but it’s not at all obligatory. Earthbag buildings can be any shape, and earthbag techniques are as versatile as any earth or bale building.
In any region with a vernacular earth building tradition, earthbag building would seem to be worth considering for self-build projects. Even in areas where the earth is not suitable, other materials might be usable after experimentation. As with all self-builds, you will need to be aware of the planning implications of what you want to do where you want to do it, and if you’re building something large enough, you may very well encounter an as yet undefined area of building regulations.
Earthbag is highly cost-effective and technically accessible, and is being used in at least one of the dwellings at Lammas Eco-village in Pembrokeshire, so it is already being pioneered in this country. The required toolkit is very simple. You can make your own tampers (a stick with a lump of concrete set on the end, or a log with a handle put into a hole drilled in it!); you’ll need a shovel, and something to cut the barbed wire with.
A quick search online will find suppliers of woven polypropylene bags, for example here, but it’s worth shopping around because even a difference of a few pence per sack could change the economics of your whole project. There are also UK manufacturers and suppliers of Raschel Mesh, for example here.
For self-build homes, community and ancillary buildings, earthbag offers an interesting and adaptable alternative. Whether it’s right for your site, or for your needs may well depend upon the present cost of small bales, because bale building would seem to be the most obvious competitor to earthbag for the attention of eco-builders.
Earthbag building in the UK is in its infancy. Whilst we have quite a number of earth builders, earthbag doesn’t seem high on their list of priorities. This means that if you’re interested enough to give it a go, you’ll be right at the cutting edge.
Thanks to Dr. Owen Geiger of Earthbagbuilding.com for information and images
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