Building Vertical Walls with Earthbags
Questions answered by Kelly Hart

Q: In order to build stable earthbag walls 12 foot tall I need a base at least 1.2 feet wide?

A: It is a rule of thumb that all earthen walls need to have a base that is at least 1/10 of the height, so yes, 1.2 ft. should work...which is easy since most earthbags are at least this wide.

Q: I like the idea of vertical perpendicular interior walls. Actually the floor plan I have in mind is roughly a 48' long by 24' deep, with a largely open interior layout but with two interior walls spaced about 16' apart to break up the space and add a little extra internal thermal mass. I assume these would lend some additional stability to that rear wall if they were tied into the foundation, etc.

A: I'm sure such walls would help with stability. Periodic rebar rods (maybe 3/4") pounded all the way through the bags and into soil and tied to the top plate for your roof, would probably assure that the wall remains intact.

Q: My husband and I live in Oregon and are building a conventional pole barn with a hefty 8' retaining wall/foundation on one end. We're wondering if an earthbag structure, with reinforcements, is possible, instead of going with a conventional concrete design?

A: It is quite possible that earthbags would work just fine for your retaining wall/foundation, but the design would need to be carefully considered to make sure. 8' is pretty high for a retaining wall, and there can be a great deal of pressure upon this, which is why reinforced concrete is a more sure approach. Two things that can help stabilize retaining walls is to curve them and also to slant them into the hill or berm. Unfortunately neither of these may work for your foundation. If the wall has to be both straight and vertical, then buttressing is an option, but this would take up space within the structure and might be problematic, unless you planned to have stalls or divisions within the barn that could double as buttresses for the earthbag wall.

Q: I have been trying to get more information about sandbag construction using ecobeams. I have emailed Mike Tremeer, the engineer that developed the system in South Africa twice. No responce either time. Is there some one in the US that uses this system that you know of? Do you know of people other than Mr.Tremeer in South Africa that I can contact? I'm not interested in the dome sandbag technique.

A: I don't know of anyone in the US using that system for building. In fact I have only heard of it being used in South Africa. I have put up this article about it: articles/eco-beam. Earthbags can be used to create a wide range of housing styles, not just domes, as can be seen by browsing some of the projects shown at that site. It is not necessary to use the Eco-beam system for most applications...

Q: I'd really like to build a cylindrical tower shaped building with, in essence, two loft levels (so three floors).  The third floor would essentially be an enclosed balcony, with walls pierced with frequent Roman arched windows.  To do something this tall, I'm thinking we may need to use double walls - perhaps just on the first floor, perhaps on both the first and second floors.  My question is this - what is a good way to tie the two concentric walls together into a monolithic structure?  Given the dimensions of the bags, which seem to have an aspect ratio or around 1.3-1.5 to 1 as opposed to the usual masonry 2 to 1, I'm having trouble envisioning something like a rat trap bond that would work.

A: I think that a cylindrical building makes a lot of sense with earthbags because of its inherent stability as a form. I do think that you could go three stories with this. Each diaphragm will contribute more stability. I would suggest perhaps the double wall on the first floor only.

You can tie these two walls together with pieces of barbed wire running perpendicular to the direction of the courses of bags. I did this when building a stem wall for my carriage house: http://earthbagbuilding.com/plans/carriagehouse.htm . If you fill the outer bags with insulating material and the inner bags with soil, this is the best thermally. The insulation on the outside will insulate the thermal mass on the inside from the outside atmosphere and make the home much more comfortable, with a stable temperature.

Q: I understand the beauty of the dome structure in earth bag construction, because it can be done without precious lumber for framing and roofs. If lumber were available on site ,would a round structure support a viga type or other wooden roof structure? Would a truss roof work without pushing the walls outward?

A: Yes indeed, vertical walled structures are possible and many have been built. For some examples see these projects. With a circular building the barbed wire that typically runs between all of the courses of bags will effectively withstand any outward pressures, and with any shape a bond beam or top plate will provide adequate bearing on the bag wall and make the attachment of trusses or vigas a simple matter. In some instances with straight vertical walls it is necessary to provide buttresses or interior walls for stabilization.

Q: If I go above ground, how high can I stack bags with no worry of them collapsing in on themselves.

A: This all depends on the design. Curved walls are inherently more stable. It is sometimes necessary to incorporate buttresses, or interior walls periodically to stabilize a wall. A cylindrical wall could probably go a couple of stories high if it is well designed...

Q: I figure to satisfy the building officials, as well as myself, I will go two and a half feet at the base and go no higher than 12 feet, getting to about 20 inches at the very top.

A: The rule of thumb with earthen construction is that the wall should be at least 1/10th as wide at the base as it is high. For a 12 foot wall, this would be about 15 inches, which is about how thick my walls were using the standard 50# rice sacks. Wider bags would be fine, especially at the base, but 30 inches seems a bit excessive.

Q: What would it happen if a wall starts leaning a little to the left, or to the right? The other day I saw this in the house. I invited a house builder, and he told me the same. He said that I should have used a "plomo." It is a piece of lead, and it hangs from a cord; they use it so the walls won´t lean. I tried to correct the leaning, and I was able to move the bags a little bit, but not enough. So, I am kind of worried.

A: It is best to try to keep your walls vertical, and using a plomo might help do this. Some slight variation is not likely to be a problem; earthbag building is not an exact science. If you are nervous about the leaning wall, I suggest that you prop it up with some braces temporarily so that it can't fall. Also, it might be possible to use a car jack to force the wall to be vertical if it is off very much. It is hard for me to say without actually seeing it. Once you have the wall up as high as you want to go and put in a bond beam up there, and get a roof on there, chances are it won't be able to move any more. The higher it is, the more danger of falling, especially if you have some questionable parts of walls. The curved walls will be sturdier than the straighter sections.

Q: If I have a room say 4m×4m with earthbag walls and I would like to roof that by timber rafters and corrugated sheets, the slope say 30cms, I mean one wall must be increased 30 cms from the opposite wall, how can I build the upper triangle using bags?

A: It is always strongest to have a continuous ring bond beam at the top of the wall, all at one level. If two opposite walls are of different heights, like you suggest, then on the higher wall an additional top plate can be securely connected to the lower bond beam, with the extra earthbags in between them. The triangular spaces on the two adjacent walls can be filled with material that tapers to conform to the angle between the lower and higher wall. This may require partially filling the bags and tamping them at an angle. A wooden or metal top plate can also be laid over this triangular section and firmly connected to the bond beam below. In this way, all of the bags are secure in case of earthquake! It is also possible to just fill that triangular space with wood or other available materials.

Q: We have a pretty big family and want to build one big circle made from earthbags with a 25ft radius, 50ft from one end to the other. We plan to cover the back of the house with earth and the south facing wall will be windows and buttress on either end and two in the middle. Do you think this will hold up? Are there any other supporting items we should include to make the house more stable?

A: A circular house with vertical walls is one of the strongest shapes to attempt with earthbags, and one that large should be fine (I wouldn't do this with a dome however). The curved shape is mostly self-buttressing, so you should be able to berm up against it without problems (just use a moisture barrier to keep water out). If the south is mostly windows, you might simply frame that with wood. Buttresses at the ends of the bag wall is a good idea. And a reinforced concrete bond beam at the top of the bag wall to strengthen it and connect the roof to is also a good idea.

Q: The idea occurred to me to buy a mobile home, place a pole barn kit around it and then place earthbags in a straight pattern running from pole to pole. The question I have is will the wall be as structurally sound as one would be in a circle?

A: Earthbags placed as infill between poles can be quite sturdy even in a straight line. You would want to secure them to the poles themselves, perhaps with the barbed wire that runs between the courses of bags. If necessary, some rebar pounded vertically through the wall at intervals and even a top plate/bond beam of wood or concrete at the top will make it even more secure.


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