Stanford University Earthbag Project

Kelly Hart and Patti Stouter fielded some questions from Stanford University students.

“I am a graduate student in the Construction Engineering & Management program at Stanford University. For one of my courses this quarter, two of my classmates and I are developing a non-profit social venture business plan. We have decided to explore earthbag construction and are focusing specifically on seismically active developing countries, beginning with Perú. Our target customers are those that are either building for the first time in an area or are rebuilding after a disaster. We are focusing on people that would otherwise build an adobe structure due to financial, technical, and other constraints. The resources on your website, EarthbagStructures.com, have been very helpful, but we are wondering if you’d be willing to answer some specific questions that we have. We are intrigued by your work, and are excited to know more about how we can help provide sustainable, safe, and affordable housing around the world. Thanks!”

Here are some questions that we drafted for you to take a look at.
1. We are researching areas in the world that earthbag construction might fill a unique niche. We suspect that they are seismically active places that typically use adobe construction despite the inherent dangers. These areas include Perú, Chile, Northern India, Nepal, Western China, and Pakistan among others. We do not know that all of those areas actually use adobe structures however. Can you confirm or refute our hypotheses as well as suggest other areas?

A: Earthbag building can be effectively used anywhere in the world, provided proper design and materials are used. Because it can be so inexpensive, using locally available, natural materials and labor for the most part, it is especially pertinent in places where poverty is common. Also, because it can be effectively reinforced for seismic events, it could offer an improvement over other methods where that may not be true. To associate EB as a replacement specifically for regions where adobe building is common may be limiting it usefulness.

Adobe, rammed earth, and cob building all use a mixture of clay and sand as the basic material. With EB, that is also what is generally used to fill the bags, but there is more latitude in the exact ratios of these materials because the bags serve to contain the material instead of requiring the walls to stand on their own. But any of the older earthen building methods can be designed with modern reinforcing methods to make them seismically resistant. I think that all of the countries that you mention do have a tradition of earthen building.

See page 26 of the Atlas of Vernacular Architecture of the World (Vellinga, Oliver & Bridge) to get a simple and authoritative answer about where adobe is used. It appears to be absent in parts of Pakistan. Rammed earth and wattle and daub are used in some parts of Pakistan (p. 24). Rammed earth and wattle and daub also occur with adobe in some of the other areas you mention. The world housing encyclopedia may have info you could use. See World Housing Net

2. We are well aware of material availability from China, but do you know if there are earthbag producers in Peru? Can we get these things locally basically anywhere?
A:Polypropylene bags do seem to be ubiquitous most anywhere in the world these days, as they are so commonly used for agricultural products. China is not the only place where they are manufactured. I know of at least one bag manufacturing plant in Columbia.
Have you looked at the info from Pisco Sin Fronteras?

3. What is the typical cost of a 4 person earthbag home?
A: There are so many variables to consider here, it is hard to give such an estimate. What would constitute a 4 person home in the US would be a mansion for many folks in the Third World, and the cost of materials and labor varies widely as well. Looking at some of the EB building that has been done in Haiti since their recent earthquake, in one instance a two-room building that could conceivably house 4 people cost a little over $2000 US…but half of this was for paying workers and the delivery of soil that might have been sourced on-site. I would say that it is possible to build an adequate structure for under $1000, but it would take dedication and resourcefulness.

4. Around how many earthbags does it take to construct a four person home?
A: Again, this depends on how you define the size of such a home. In the case of the home in Haiti that I mentioned, they used 750 bags. Here’s how you calculate How Many Bags Does it Take?

5. In construction, do you find that masonry or wood piers are necessary to frame the earthbag walls or can the earthbags form a wall by themselves?
A: Earthbags can frame a wall by themselves, but certain rules need to be followed to safely do this. See EarthbagStructures.com for more about this.

6. Do you find that earth bags are a cost effective solution in developing areas?
A: Yes, indeed this has been proven already.

7. Are there data to confirm the seismic performance of earthbags?
A: Not as much as one would hope. The testing that we know about is outlined at EarthbagBuilding.com and new experiments and testing is under way at this time. Much more is needed!

Earthbag has good compressive strength. It appears to be stronger than adobe (tensile strength of the barbed wire, tamped rather than poured mud has greater strength, rebar bonds with tamped earth bags as it is driven in, in contrast to reinforcing rods that are inserted into holes in adobe, flexibility of individual bags anchored on barbs greater than the brittle mortar used in adobe).

Patti’s summary of structural issues is still accurate, although recent tests with wind tunnel and planned shear testing (U Cincinnati hopes to get some done) may add important data. See
http://www.scribd.com/doc/38259520/Friction-Tensile-Strength-of-Earthbag-Components