The type of roof you choose for an earthbag house is important. No matter whether you construct a circular house or a rectangular one, you want to take into account your roof before you build (or be prepared to alter your roof style at the end).

I won’t deny it. When it came to my earthbag roof, as is so often the case with me, I skidded to success by the seat of my pants. It was sheer luck I chose the right type.

Roofing structures exert a lot of pressure onto earthbag walls. This is fine if the pressure is in the right direction because earthbag walls are strong. What you want is the pressure exerted downwards. What you don’t want is it pushing outwards.

The safest roof type for earthbag
If you are a beginner, the safest, most foolproof roof to stick on your earthbag house is a flat or skillion (pitched) roof, utilising horizontal joists running the length of the building. The joists act as a type of grid that pulls the structure together and prevents the walls falling outwards. What’s more, if you’ve built a smallish round house, you won’t even need a bond beam! You could top the joists with a number of materials: Corrugated iron, ply/strand board with a membrane. Any weight on the roof will be distributed by the joists and easily supported by the earthbag walls. The pressure exerted by such a roof is downward.

The link below shows another example of an alternative reciprocal roof on an earthbag house. Notice how this team combined two styles here. While the main structure is reciprocal, a web of rafters has been inserted into each facet of the roof. Those rafters then form the all-important grid through the top of the earthbag wall which locks the whole structure together.
http://mylittlehomestead.com/ep12-undergound-earth-bag-construction-reciprocal-roof-facia-frame-complete.html

Why you don’t want a compression roof
Compression roofs are typically used for yurts. The design of a compression roof means the strength of the roof structure is derived from the compression between an outer ring or wall, and an inner ring. Such a roof is exerting a lot of outward pressure on your earthbag walls.

If you know what you’re doing, there are of course a whole gamut of other wacky and exciting options for earthbag house roofs, and you'll be able to customize many to work for earthbag. But presumably, if you know all about roof construction, you're not reading this post.

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Remember Gautam and Kim from our crazy earthbag house in 7 days adventure?
Only eighteen months on from that workshop, and these two are already well into constructing an earthbag empire over in India. They have completed their first earthbag house, as well as planting 350 fruit, flowering, and indigenous trees to create a diverse food forest, and a vegetable garden too. But the project wasn’t without its challenges. I’m so grateful to Gautam for letting me share his experience, because it’s rammed full of great lessons.

​What Gautam posted in our Facebook Group:
​
“I’m happy to say my first earthbag structure endured its first torrential monsoons. We witnessed over 3m of rain. I have attached a video taken after a storm (over 13 inches of rain in 24 hours!) where most of the land is flooded, and with the rubble trench foundation working like a charm keeping the interior bone dry.”

Fantastic work Gautam and Kim! The rubble trench foundation combined with gravel bag stem wall is THE way to deal with earthbag buildings in wet climates. I’ve suffered various disbelievers regarding the amount of flooding an earthbag house can withstand, but a properly built earthbag house with the right footings can literally handle a monsoon. Had Gautam followed mainstream building advice and used concrete instead of gravel, I guarantee that water would have wicked up the earthbag walls.

But of course, it hasn’t all been plain sailing.

“Lime plaster on the other hand has been tricky for me. The first time we completed the lime plaster was about two months before the monsoons and it seemed to hold up well initially…till it didn’t, with chunks falling off from sections of the wall….On the plus side, there are certain portions where the plaster is rock hard and no touch ups have been ever needed.”
​
Agh plaster! I always say it’s the most difficult part to master. And in a wet climate? Really tricky. After a little further investigation and some more photos, I could see Gautam’s plaster was holding up fine on the stem wall. This was because it was gravel. I realised Gautam and Kim were having the same trouble I had had with my earthbag house, but on a more intense scale. 

What was happening?

Gautam and Kim’s earth’s composition was a staggering 50% clay! Normally you’d want around 20-25% clay in your earthbag mixture. In a dry climate it wouldn’t really matter. But in the wet? Clay swells when it gets wet, and shrinks when it dries. The clay inside Gautam and Kim’s earthbags was expanding like mad in the monsoon, and then shrinking back in the dry season. Lime plaster on the other hand doesn’t swell or shrink. So when the earthbags expanded, the lime plaster cracked. Had they used concrete, the result would have been exactly the same for exactly the same reason.

What can be done?  

​I found with my own earthbag house that it took a full dry season for the entire structure to completely dry out. Once the earthbags had dried thoroughly, I plastered again at the beginning of the next dry season, to give the plaster a good five months of baking before winter arrived.
​
My plaster wasn’t simple lime render though. It was clay/sand/lime/straw. 

What will Gautam and Kim do?

There will be some trial and error. I think they’ll probably need a clay/lime/sand plaster which is light on clay and heavier on sand. The lime will help rid the plaster of moisture when the monsoon hits, the clay in the mix gives a bit of flexibility to the plaster, and the sand gives the strength. It will, however, depend on Gautam’s clay as to how well it works with the lime.

The Next House

Oh, once the natural building bug gets its teeth into you, it doesn’t let go! Gautam is already laying the foundations for his next earthbag house.
​
“We just finished the stem wall for another 6m diameter roundhouse using local laterite rock with a lime mortar. We will be starting on the earthbag walls soon and I was wondering if lime should be used to stabilize the earthbags considering the plaster issues with the other structure.”

This, in my opinion, is an excellent idea. Normally you’d use 10-20% lime in stabilised earthbags, but in Gautam’s case, I think I’d go 30% and try and get rid of as much of that clay as I could.

Gautam has plans for a living roof on the top of this house. I can’t think of a better climate for it, and I look forward to seeing the result.

Lessons Learned

Now, if there’s a man who does a job well, it’s Gautam. He researched this mission carefully, worked out the best structure for his climate and location, asked for help when necessary, and got his hands dirty in live courses. As I think is pretty clear from the outcome, he really knows his stuff. Yet he still faced challenges.

So...if you take one thing away from this build, I hope it’s this: even if you’re an expert, you’re going to be greeted by something that doesn’t go to plan. The folk who manifest mud worlds are not those who don’t have problems, they are those who face them, and work patiently and persistently to overcome them.

You have read this post thanks to The Mud Home Sustainers and all those supporting this site, be it with contributions, positive and constructive feedback, or by sharing. If you’d like to join our Mud Home group and enjoy the perks that come with it, hop over to my Patreon page.

​Normally, earthbags are filled with damp earth. The earth should have about 20-25% clay in it. If you are using bags rather than tubes, then you first fill the bottom of the bag and squash the damp dirt into the base and corners to create a nice square bottom. After that you fill the rest of the bag, and lay it on your wall. When all the bags in the row are laid, you tamp the entire layer with something heavy and flat. Tamping is key. It squashes the clayey dirt into a compacted, immovable layer. Eventually, when the house dries, that dirt becomes a solid clay brick. 

All of the above is pretty time consuming, and dragging bags full of damp dirt around is hard work. Under normal circumstances, and to prevent a hernia, once the wall gets higher you begin filling the bags on the wall itself. Again, this is pretty slow going, and can drive impatient types like me mad.

I say, there’s always another way. :) Last year in my earthbag workshop in Turkey, we stumbled upon a brand new technique, altogether by accident, and it changed our earthbag world. You know how it is; someone makes a mistake, and it ends up being the best thing that happened.
 
The mistake was that a few volunteers threw a row of earthbags onto the wall without dampening the earth first. As I went round and prodded the bags, I could feel they were bone dry. Just a bunch of loose aggregate. You can read why you don’t want loose aggregate here.
 
Now...there is a common misconception that the polypropylene bags usually used for earthbagging aren’t breathable. This isn’t correct. They are definitely breathable and permeable. If they weren’t, your dirt wall would never dry out properly. So, knowing this, I decided to try and wet the bags on the wall (well, actually I decided someone else would wet the bags, but you know what I mean).
 
A kind helper grabbed a hose and gave the dry layer of bags a really good soaking. Then he grabbed the tamper and tamped the lot down. When I checked the bags, they were as good as the rest. The bags had absorbed the water, and the tamping had distributed the water evenly through the earthbag.

The advantage of wetting the bags on the wall is that you don’t have to cart all that damp earth about, nor do you have to dampen the earth on the ground and mix it in (which is a bit of a bind in itself). It is a lot lot easier to work with the loose dirt, and easier to fill the sacks, too. 

1. Make sure your clay is distributed evenly into your dirt.
2. Fill your earthbags with dry soil.
3. Lay them on the wall.
4. Take a hose and give the whole layer a thorough wetting. Make sure all the bags are well dampened.
5. If you’re using individual bags, go around and check the corners of the bags are nice and tight, and not sticking out. Reshape and regusset them where necessary.
6. Tamp the whole layer.
 
Note: This technique only works by dampening one layer of bags at a time. Don’t throw a whole house up and then think you can squirt a hose on it. It won’t work.

​You have read this post thanks to The Mud Home Sustainers and all those supporting this site be it with contributions, positive and constructive feedback, or by sharing. If you’d like to join our Mud Home group and enjoy the perks that come with it, hop over to my Patreon page. 

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.

​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.
 
The foundations
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.

​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.

​If you want to know more about the kinds of mistake you can make while building an earthbag house, you may be interested in my most popular book, Mud Ball. This is the story of how I built my own earthbag house, and the various agonies I and the victims I managed to lure into helping me, endured in the process. The ebook is on offer this week at $3.99 on all ebook retailers in all locations (including Kindle, Nook and ibook) so if you’d like to catch it at this lower price, now is your chance. It will go back up to $5.99 on 24th December 2017.

“Despite having very little money, almost no building experience, and endless naysayers who told her she would fail, Atulya K. Bingham completed her lovely earthbag home . . .Her personal, inspirational story shows how anyone can build their own sustainable home with earthbags." Dr. Owen Geiger, author of Earthbag Building Guide and the Natural Building Blog. 

Many thanks to Baykal for keeping track of the figures for us.