Earthbag building is probably one of the least technically taxing construction techniques you can choose. You can get away with having no experience whatsoever and still build yourself a strong, sound home. That said, I have seen a few examples of things going wrong, and it’s always the same mistake, so I thought I’d shine a spotlight on it.
Everyone worries about the wrong thing, and I was exactly the same. Most questions come to me concerning foundations, climatic impact on earthbags, and bag fillings. This is probably because folk are at the outset of their build and still planning. Once the construction begins, the questions tend to evaporate in the excitement.
Things not to lose sleep over:
The bag filling is not nearly as crucial as you think it is. As long as you’re using dirt, and that dirt is basically sticking together when wet, you’re going to be fine, (see my article on bag fillings). I did recently spot some birdbrained article by someone who had clearly never laid a finger on an earthbag, claiming you put straw in the bags. Obviously that would be a bad idea. Earthbags are for clayey earth.
Now I’m not saying you don’t need to think about foundations. You do. But we’re all somewhat brainwashed by mainstream building techniques, and convinced the foundations are the linchpin preventing the house from falling down. We’re also certain that that there has to be a concrete slab somewhere, because that’s strong, right?
In fact, a whole bunch of things contribute to the structural integrity of a house. With earthbag building, the foundation is as important for drainage as it is for structural strength. Forget the concrete slab. Forget concrete full stop. It really isn’t what you want or need. Make yourself a nice simple rubble trench with a couple of earthbag rows below grade, and you’ll be fine. It’s simple, effective, and hard to screw up.
The most common mistake is for a wall to collapse.
The most common earthbag issue by far is for a wall to topple. This notably only happens with square/rectangular structures or very large round structures (more than 10m diameter), or retaining walls. So if you’re new to the bagging game, you might want to consider a smaller round house first.
If you’re adamant you want straight walls, then you’ve got to pay good attention to a few things:
1. You need buttresses. And the buttresses must lock into the wall and be attached to the barbed wire of each layer. So you can’t just say, “Oops maybe I need a buttress here,” and add one at the end. It has to be incorporated into the build. This equally true for retaining walls. The higher the wall, the more buttresses you need. A rule of thumb is a maximum of 10 feet/3 metres between buttresses.
2.Your vertical straightness is crucial. With a small round house you can get away with an awful lot. With a square/rectangle, those walls need to be vertical.
3. You need a decent bond beam* to lock the top of the structure together, and on a square structure, that would mean long, straight planks of wood nailed into the top layer of bags.
The logic behind earthbag strength
Every building technique has its own logic, and its own way of supporting itself. With earthbags, the structural strength of the building is created by the ‘tying’ together of everything within the structure using barbed wire. Everything – every bag, every window frame, every door frame, every arch and buttress – must be attached to the rings of barbed wire so that the entire structure is interlocked. This is what really gives it the tensile strength when under pressure of impact or earthquakes, and what stops the walls from toppling over.
If you want to assess whether your walls are liable to collapse, climb on the top of them or give them a shove. If there’s any swaying, you’re in trouble.
Finally, at the end of the build, make sure you have two layers of earthbags going over the top of everything (lintels, arches etc.) Those final two layers create enough pressure and tension to hold the structure together. In most cases you will also add a bond beam* here too.
I know some people are using mesh bags, and I have to be honest, I don’t see how the structural integrity of the building is maintained, especially in seismic areas where the house sways. If someone has actual hard-won experience (rather than hearsay or armchair opinion) of using the mesh bags, please add your findings in the comments below.
*A bond beam is a horizontal reinforcement that runs along the top (or sometimes the middle) of a wall. It holds the wall together and stops it breaking open. In modern mainstream construction, concrete and rebar are used. In traditional building it has usually been thick wooden planks or beams. Don’t assume concrete is stronger. It is brittle, and in the case of an earthquake it can crack. The rebar is the only thing giving concrete any strength. In my opinion, for an earthbag structure, wood is a better option. It has more give, and can move with the house in the case of a quake.
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