Earth and clay, in and of themselves, are not insulating materials. They have thermal mass, which means they store heat (or cold), but don’t reduce the transmission of heat energy from inside to outside (or vice-versa). Nevertheless, you can make earth plaster more insulating if you need to. More on how to do that, and how well it insulates, later in the post.
Insulating a House Basic Overview
Before I get to the plaster game though, a quick overview of insulating houses in general: The first thing you need to worry about is not the walls, it’s the roof. That’s where 60% of your heat goes. High ceilings are notorious for energy wastage, as you have a fat layer of completely unused heat that skulks under the ceiling. Your floor is the next worst culprit for heat loss. This doesn’t mean you don’t want to insulate the walls. You do. Though sometimes insulating the north facing wall (or south facing in southern hemisphere) is enough. But insulating the walls without sorting out the roof is a bit pointless.
What is all this jabber about R and U values? If you’re a newbie builder you may be wondering. Insulation levels are measured in R values. Here’s a neat little infographic for US climate zones showing the kind of R values you would need for your roof, floor and walls for a conventional house in various climates. All building materials have an R value per inch, though be careful because calculating R values is a bit more complicated than just multiplying by inches. Some insulating materials work in different ways (for example, if you compress certain materials, or mix them into something like clay plaster, then you reduce their capacity to insulate). Nonetheless, the graphic gives a basic idea of what’s going on with R values.
Then there are U Values, which rate how energy efficient a given system will be. Me? I want to get back to earth plaster, but if you feel like geeking out on U Values as well here’s more info.
Ok, back to the plaster. First, let's be clear; Mixing insulating materials into your earth plaster alone isn’t going to cut the mustard in seriously cold climates. You’ll want to use the Other Ways to Insulate an Earthern Wall listed in the next section. But if you live in a temperate climate, or a place where you need a little extra oomph in the winter months, insulating plaster can work a treat.
Note: When using insulating plaster, you need to apply a thick layer (at least 3 inches). It's important to add the plaster to the exterior walls of the house for maximum insulation (though if you’re restoring a listed building, this may not be possible, in which case you’ll have to insulate the interior wall instead).
Other Ways to Insulate an Earthen Wall
If you live in a climate which remains below zero for months at a time, earth plaster alone is not going to be enough. I'm not discussing whether or not you should have built a mud home in a cold climate here, nor going into massive detail. There are a few ways of insulating earthen houses. Most of these require attaching a light lath or frame over your wall, and stuffing it with some sort of insulation such as:
Alternatively, you can cover the exterior of your mud house in straw bales (R 1.45 per inch).
I'm sure there other natural, insulating earth plaster methods out there. If you've tried something else, feel free to add it in the comments.
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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. You might even be fine if it isn’t sticking, because the bags are holding the dirt together (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 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.
Special Christmas offer until December 24th.
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.
The great thing about being on the road is that you finally have the chance to visit other natural homes. Many of them are inspirational. All of them teach me something new.
Abrazo House is a cob/strawbale hybrid tucked away in the sweeping Cantabrian hills. It’s a perfect example of a well-built natural ecohome, with a green roof that flourishes in the wet climate, earth plaster created from clay on site, and a lime wash finish to protect it. The lower floor is made from insulated cob, and the upper floor is straw bale. It is, as you can see, quite beautiful. At 200 square metres, Abrazo House is the largest self-built natural home I’ve seen so far.
Robert, the creator of Abrazo House, has executed a number of impressive eco building projects to date. There is a cob cabin on the land too, and just up the road he has two more fabulous straw bale houses on the go which will ultimately be sold. Indeed this is something of a natural house empire with a view to breathing life and community back into an abandoned Spanish village.
But here’s a little secret just to encourage folk. Something went awry in the build of Abrazo House (which if builders are honest is par for the course in construction). And what do you know? I have something interesting to write about, and we all learn something new.
So what went wrong?
Originally Abrazo house was planned to be completely straw bale. Because the climate was wet and the build took a long time (four years in total), by the time the second floor was reached, the first floor had begun to rot. I don’t want to imagine how Robert and co. felt the moment they realised this. Personally, I would have lay down in the dirt, beat my chest and howled for a day. But Robert seems a mellow chap, so he probably flipped a little more quietly than I would have. And anyway there is always a solution. Many times it becomes the most outstanding feature of the house.
How did he solve the problem?
The issue was resolved by jacking up the first floor, removing the bales and then creating cob walls in their place. The cob easily supports the bales (which are far lighter than the solid earthern walls). Thus this has become a rather magnificent example of a hybrid natural home.
How did he increase the insulation value of the cob?
The reason Robert chose straw bale in the first place was that he was concerned about insulating such a large house. Straw bale has a high insulation value. Cob, on the other hand, has a high thermal mass value but is not particularly efficient for insulation (you can read more about that here). To mitigate this issue, Robert replaced some of the sand in the cob mix with sawdust. The result is a fabulous, attractive and warm family home.
Is this house built to code?
For those ever hungry for information on legalities: This is a natural home built to code. Yup, fully legit (as we say back in Essex). To do this in Spain you must buy an appropriate piece of land (edificable), speak to officials in your local government, get an architect to draw up an official plan, and then have it signed off by various titled pen-wielders in various offices. Obviously, each time you take any of these steps you will need to inhale and exhale deeply, and spend some money too. Patience and persistence are the two characteristics you must cultivate when embarking on a self build project anywhere.
Something else I learned:
Robert was mixing his earth plaster using an unconventional method (at least I’d never seen it done this way before). We laid a large layer of gravelly sand directly on the ground, then added a layer of clay, and finally some straw. Then the ingredients were mixed using a rotavator. Unfortunately I have no photographic evidence of me doing this, which is tragic because it was truly a battle between woman and machine:) To use this method successfully you need a fair bit of experience with earth plaster first, so you know exactly how the mixture should look. It’s quite hard to measure the quantities of ingredients carefully when they are spread on the floor. But because Robert knows his dirt and his climate well, he knows from sight and can assess the state of the mixture just by handling it.
If you want to read more about Abrazo House, or would like to help volunteer, go to www.abrazohouse.org.
Insulating cob and earthbag houses. And do you need to?
“I live high in the mountains, and it snows regularly. Will earthbag be warm enough?” This is the type of question I field on a regular basis. So are cob, mud or earthbag homes good for cold climates?
The short answer is no. The long answer is hybrid. But first, it pays to properly grasp the difference between thermal mass and insulation.
Thermal Mass (Earthbag, cob, wattle and daub, and adobe all provide thermal mass).
Earthern walls provide thermal mass. This means they absorb the heat and store it (at a rate of about an inch of wall an hour). If you are in a warm, dry climate with plenty of sun this is what happens: The house absorbs the sun’s heat in the day, and then at night when the temperature drops the walls radiate the heat back into the house. By morning the earth has released all the stored heat and has absorbed the cool in its place. So now in the heat of the day the opposite occurs; the walls release cool into your house. It’s a type of natural air-con. I experienced it with my own earthbag house in Turkey and it was quite wonderful.
But...you need sun for this to work. If you live in a cold, wet climate, this system won’t benefit you because your walls are going to store cold air instead, which is not what you want.
Insulation (Straw bale insulates)
Insulation is different. It slows down temperature exchange (heat or cold are prevented from moving through the wall). In the natural building world straw, saw dust, reeds, hemp, wool, and paper are the most common insulating materials.
With this in mind, typically you would be advised to build a straw bale house in a colder climate, and an earthern house in a warm, sunny climate. But not everything in this life is typical. In fact there are an awful lot of extra factors to consider.
Quirks and exceptions to the rule.
1. Cold climates are often lumped together in the thermal mass discussion. But in my experience the real killer for earth is cold with no sun. Back in my earthbag house in Turkey, I remember the temperature dropping to -7 degrees celsius where I lived, but because the sun was shining, and I had south facing windows which acted like a greenhouse to catch the solar warmth, the walls still absorbed that solar heat and despite the subzero temperature, I didn’t have to burn the fire until the sun began wane.
My personal experience was as follows: My earthbag house was always warmer on cold, sunny days than on cloudy days. I had to light the fire on rainy days even though the temperature was actually a good ten degrees higher than on cold clear days.
2. Earth will cope a lot better with the cold if you live in your house permanently, and therefore heat it regularly. As mentioned the walls retain the heat. The thicker the walls, the longer they retain it. Over time the house gets warmed to the core, which can carry you over a shortish cold spell. The trouble is of course, if you leave your house for days on end it also gets cold to the core, and may take a couple of days to heat up.
Conclusion: If you are building a weekend holiday home, or a community centre that is not continually lived in, and you are in a cold, grey climate, you will desperately need insulation. On the other hand, if you are building a smallish mud house, with excellent passive solar design, you live in it continually, and the temperature is not perpetually subzero but goes up and down with plenty of sunshine, you may well get away with it.
What if you live in a cold, non-sunny climate and still want an earthen house?
There are reasons you may not want to build a straw bale house (I have a straw allergy for example). So what you need to do is create a hybrid, and insulate your mud walls. How far you insulate will depend on how cold your climate is. You could create a straw-heavy earth plaster for your walls, or coat them in some sort of papercrete. Some people have attached reed mats to walls and plastered over them, Or lined the walls with straw bales. Someone suggested creating a lath and stuffing it with wool, or straw. Cork can also be added to the render, or to a lime render (thanks to Cath Coffey for that one;)
Long before I built my house, back when I was setting up a yoga camp on Turkey’s Faralya coastline, fellow builder Chris Shaw said to me, “The land will tell you what to build, it’s all about the land.” It was an aphorism that adhered itself to my brain. And it has served me well.
Following the land is what humans always used to do when they built homes. Before settling anywhere or building anything, we would scan the topography of our terrain, discover which materials it had available, which climate it was in, and which gifts it had to offer. Because land always comes with gifts. The modern approach of marching in with a bulldozer, razing a plot to the subsoil, and then slapping down a whopping great cement slab is a very recent phenomenon.
Ten days ago while on my quest for new land, I stumbled on a perfect example of how ancient humans used to work with nature to construct houses...in France.
La Roque Saint Christophe in the Dordogne is a fascinating place for a natural builder. Humans have been living on and in La Roque for at least 25 000 years, so the place acts as a wonderful chronology of construction.
Initially, the troglodytes used the contours of the rock to live in, sometimes with animal hides tacked up like tarps.
Then a new technique arrived: Wattle and daub. It’s estimated wattle and daub has been around for as long as 6000 years. In La Roque Saint Christophe, the builders of the day would carve out niches in the rock and insert large beams to create a post and beam structure that jutted out from the contoured rock. This gave them more living space. Then they filled in the structure with a lath and mud daub, or with wooden shingles.
Later, by medieval times, builders replaced some of the wattle and daub with cubes of rock to create even stronger structures, and the troglodyte city became a sophisticated fortress, with roads, drawbridges, and cranes.
It was purely by chance that I found La Roque, and it is an exquisite illustration of natural building through the ages. So if you’re ever in the Dordogne in France, go have a climb around. You can find out more about La Roque Saint Christophe from their website.
A superbly useful interview with Kim Siu of the charity Get Rugged.
There are two ways of building yourself a natural home, no matter which country you are in: The unofficial way. And the official way.
The unofficial way involves skirting round the edges of the system, finding loopholes and sliding deftly through them. (I’ve seen this done in every country I’ve been to so far, though while entirely possible generally appeals to more risk-taking type of personalities).
Then there’s the official way. This costs more money, but may buy some peace of mind...in the end:)
Kim Siu, who runs the self build charity Get Rugged up in Scotland, built her beautiful straw bale house the official way. I was lucky enough to stay in that house, and talk to her. Here’s what she had to say:
Atulya: What do you think is the most important thing you need to build a house to code?
Kim: Sheer bloody-mindedness, and determination. That’s the number one thing you need. You mustn’t get ground down, and always keep telling yourself there is a way. Because there usually is. Even if you have to compromise. And sometimes we have to compromise in life. It’s just like that.
Atulya: I completely agree. You need determination no matter how you build. There’s always a way. There’s no problem without a solution. And sometimes you might have to change your vision slightly, but the basic core of it remains.
Kim: Yes. We kept our vision strong, but we just had to do little pivots every now and again. We found that working with the system, rather than trying to go against it really helped. We got the planners in from the very first stage, before we even parted with a penny. And then we did a staged approach, so every time we got some designs I’d go and speak to the planners, and show them what we were doing. Now we’re doing another build, so we’re doing exactly the same. I spoke with the planners. She came on site. I’ve showed her the early stages of the concept. And again, every time we develop the designs, we’ll take it to her, and she’ll give us her feedback. It’s actually really good, because you get a lot of foresight, which you don’t have to use as hindsight:) She’s not worrying us. She’s making us aware of things. Like road access, and different conditions. So we’re not surprised later on.
Atulya: Yes and you’re not forking out loads of money first, and then regretting it. So let me just clarify. It is totally legal to build a straw bale house in the UK, right?
Kim: Oh yes. Absolutely.
Atulya: So what did you have to compromise on?
Kim: We had to compromise on window sizes . They wanted the larger ones on the bottom. They wanted everything to be symmetrical, and didn’t like anything too quirky, because it has to fit in with the local vernacular. If you were somewhere else, like Findhorn where there are more alternative buildings, you’d have more freedom It’s very area dependent.
Also planners need to be dealt with on an individual basis. You’ve really got to develop a good relationship with them.
Atulya: Yes. That is the same everywhere. Relationships are key.
Kim: There are two government bodies you have to deal with: planners and building control. Planners deal with things like local vernacular, and you have some flexibility here. You can appeal their decision too. But building control is different. It’s the nuts and bolts of the build, your house’s sustainability principles, it has to meet various regulations. They want engineer’s certificates and things.
Atulya: Did you have to make compromises there too?
Kim: Oh that was the worst bit! In our build, there was an architect, a builder, and an engineer all talking to building control. This meant it turned into a very complex process. It could have been simplified by using a design and build company, because they design the building they’re going to build. Then you know exactly how much it’s going to cost, and it’s easier.
Eventually, I went to the building control officer and asked, “How can I make this easier for you to put us through building control,” and he said, “Get your architects and get your builders, and get them all sat round this table.” Really clear communication is essential.
Atulya: Does building control happen while the building is being constructed? Or before or after?
Kim: You can’t even dig a hole until you have a building warrant, and it took us about 18 months to get through both planning and building control.
Atulya: What advice would you give to anyone wanting to build a natural home the official way?
Kim: Either get a design and build company (the easy option), or if you’re going to build it yourself get a team you can work with, get people (engineer/architect) who know the codes and can help you get through planning.
Atulya: And the cost?
Kim: The charge is dependent on the cost of the build or the cost of the site. It’s proportional. So you’re talking several thousand pounds before you’ve even broken the ground.
Atulya: Which is more than my whole house cost! But there are advantages to doing it this way. What are they?
Kim: They’re not going to pull your house down. Mine is a family house. I’ve got four kids. I’m on a B road. People drive past us, so we’d have got told on before long. You have more security this way. In truth though, the main thing was to get a mortgage. We couldn’t have got a mortgage any other way.
Atulya: There you go. I didn’t know that. So you can get a mortgage even on a self-build natural home project?
Kim: Yes. Though only certain places. We got ours at the Ecology Building Society.
Atulya: And any last tips to close on?
Kim: Create decent relationships with everyone. Planners and building code officers are human beings too. Don’t annoy everyone too much. It’s OK to dig in sometimes for something you really want, but treat people kindly, and with respect. It goes a long way.
Getting permission to build a natural home in the UK. What you have to do:
1. Get planning permission. Call in a planning officer at the beginning to look at your site, and make sure you’re able to build on it. Some tests (drainage) are done at this stage.
2. Gather an experienced team (design and build company, or an architect/builder who knows the ropes). Go for your building warrant through a building control officer. (You can apply for planning and a building warrant together.)
3. Once you have a warrant, start building. Building control will turn up at intervals to check things.
For more information go to GET RUGGED, and pick up the free self build PDF. Or connect on Facebook.
IN THE USA? It's a very similar story. Here's an article by Sigi Koko on how to build to code in the US.
Do you find these posts valuable? If so please consider supporting me on Patreon so that The Mud Home can continue. You can give as little as $1 a month (less than half a cup of coffee). Many thanks to those who are already Mud Patrons!
Over at Rubha Phoil, a sustainable lifestyle project on the Isle of Skye, I had the opportunity to use another type of composting toilet. How lovely! This one was designed for several people to use, with a wet climate in mind.
All composting toilets work in the same way. The key is to keep the crap dry by adding plenty of aggregate. Sawdust, peat moss, cool ash, coconut coir, and dry leaves are all great aggregates.
In the Rubha Phoil toilet, the poop goes in one place (the bucket with the white lid), and the urine in another (the yellow bucket under the blue chair).
The bottom of the poop toilet has a hole, and that goes into a large wheelie bin, which is very practical for emptying. When the bin is full, it is emptied into a composting area, and left for 6 months to a year. This allows the pathogens to neutralize. The result is quite amazing; a peaty, fresh smelling compost perfect for gardening.
Composting toilets are insanely easy to make. They cost next to nothing, and turn your crap into gold. I’ve even got one in my van. It took me about 2 minutes to put together.
All you need for a makeshift composting toilet is a bucket, a toilet seat and aggregate. Line the bucket with a good fat heap of sawdust (or whatever you have to hand), then begin using.
The key to preventing unpleasant smells is the amount of aggregate.
Do you have to separate your urine?
This depends on your climate, your type of composting toilet, and how much aggregate you can lay your hands on. I never separated mine in Turkey, in my simple box style composting loo. In a very cold, wet climate (Scotland) I'd say separating is advisable. But if you have enough sawdust/ash etc, you can get away with some mixing.
The Bottom Line
Throwing the world’s most precious resource (clean drinking water) in a flush toilet, and then mixing poop into that clean water to create a polluted, pathogen breeding mess which then requires a treatment plant that squanders megawatts of energy to neutralize, is nothing short of mass lunacy. Some day it will be called an ecocrime.
How much does it cost to build an earthbag house?
It’s the question I love to hate. But I’m asked it a lot, and I understand. People want a ballpark figure before they decide if such a house is for them. The truth is, you could spend a thousand dollars on an earthbag house, or a hundred thousand. It depends on many many things. So before you zip over to that contact form to ask me, read on.
(A cost breakdown of our last earthbag build in Turkey 2016, is below)
1. What type of earthbag house are you building? A ten-bedroom castle, a school, a shed?
2. Are you paying for manual labour? Or do you have volunteers?
3. Which country do you live in? Are materials cheap there? Are skilled workers such as carpenters expensive in your country?
4. Are you a perfectionist? Or are you fine with a few lumps and bumps?
5. What kind of roof are you making? The roof is the most expensive part of the build.
6. Are you building a round house (less expensive and stronger) or a square structure? Post and beam? (The more wood in your build, the more it's probably going to cost).
7. Are you trying to build to code, or are you winging it?
All these factors are going to impact greatly on how much your house will cost. So, the short answer to “How much does it cost to build an earthbag house?” is “I’ve no idea.”
How can you estimate the cost? I decided to publish a breakdown of the cost of the 5.5 m diameter round house plus bathroom, we built in our earthbag building workshop in Turkey last year. (Thanks to Baykal for keeping a record of the figures).
But there are a number of things to take into account.
1. This was Turkey. As you will notice, some things are very inexpensive, others not so much. If you are in the UK the labour is going to look incredibly cheap. If you are in India, it's going to look expensive.
2. We used some of the earth from the site and some with a higher clay content was shipped in (roughly half and half).
3. We used more lime than you are ever likely to due to odd climatic conditions in our region. Thankfully lime is as cheap as chips in Turkey. In fact, now I think about it, per kilogram it's cheaper than chips!
4. At the time of writing, most of the exterior and interior plaster work had been done, but the floor hadn’t been laid and the bathroom was only half completed. The roof will receive a thick layer of clay on it too. So extra costs will certainly occur over time.
5. With the exception of the roof, the house was built almost entirely with volunteers and course participants.
Cost of the earthbag round house without roof.
Figures in US dollars based on the Turkish lira exchange rate at the time of writing.
Total house price = approx $ 6250 USD
Note: We estimated that if we had made a simple living roof as on my own mud home without employing a carpenter, such a roof would cost about 1000-1500 USD. In which case the total house price would be nearer to $3000 USD.
One thing I’ve learned is this: No matter how much you calculate and research, be prepared for your budget to be blown. For some mysterious reason (quantum physics? The illuminati?) all construction seems to cost twice as much as you estimate. Things take longer than expected. Other things go wrong. It’s just like that. So allow some nice wide margins in your budget. Or end up like me, and have to step back into the daily grind for six months to earn the money to finish.
Many thanks to Baykal for keeping track of the figures for us.
Last week, as luck would have it, I ran into a two natural builders tucked away in the hills of central Portugal. Lucky me; they showed me around their fabulous cob creations (not to mention plying me with vinho frisante and humous).
Take a look at this wonderful cob oven with cob seating area Frenk and Nicole built. It's gorgeous. But that's not the half of it. It's also water-resistant. The area containing the cob oven and seat isn't protected from the rain. Yet the cob has stood its ground.
How did they do it? They coated the entire thing in 3 layers of linseed oil. I'd heard about linseed oil from a few Mud friends in India where the stuff is cheap and easy to find, but I'd never tried it myself, because in Turkey the cost was prohibitive, more than organic olive oil!
"Yeah, it's not cheap here either," Frenk lamented to me, but good on him, he tried it anyway. "You heat the oil in a pan first, though not to boiling point. Otherwise the brush melts,” he explained.
Frenk and Nicole made their cob mixture out of clay, straw and sand. Initially, like me, they imported the clay. Then they realised the local earth was clay rich, and a glorious rust colour to boot.
Frenk is something of a rocket stove wizard, and has engineered another in his kitchen. If you want to look around it, check out the video. It’s very informative. The guy should have his own channel:)
This is a question that seems to come up quite a lot in various forms, so I’ve decided to write a post on it.
What Can I Put in my Earthbags?
The answer is: It depends what you want to do with them.
If you want superadobe, which is a specific technique to create solid clay/mud bricks by allowing the mixture to cure on the wall, then you need an damp earth-clay mix. About 20-30% clay is ideal. The mud needs to stick together in a ball when you roll it in your hand. It shouldn’t be breaking up like oatmeal.
What’s the big deal about superadobe? With superadobe, the earthbags cure on the wall, and once dry are rock solid WITH OR WITHOUT THE BAGS. A friend of mine forgot a stove pipe hole in his superadobe wall. In the end he had to dig out a hole with a teaspoon because the walls were so darn solid. He said it was like escape from Colditz:) You could burn the bags off, and your building would stay standing.
Experiments have shown you can add things into the damp clay-earth mix without too much impact, especially if the bags are left intact. Stones less than an inch (2-3 cm) in width can be left in. Some people have added things like pumice for insulation.
Stabilized bags for foundations.
You can mix your mud with lime to stabilize it for foundations, which obviously see a lot more water and pressure than the rest of your walls. You can also fill them with limecrete, gravel, or a mixture of both for the foundations.
Can’t you just fill the bags with sand? Or stones? Or any loose aggregate?
In theory, if your earthbags are tough and hold, you could put anything in them. The army have been building sandbag bunkers for years. They’re strong, bullet proof and safe. But here’s the thing. Rip those bags open and you have...you got it. A mess. There are a number of ways the bags can lose their integrity: Polypropylene bags deteriorate fast in the sun. Jute bags tend to rot if used in damp climates. And if you happen to have mice attempt to move in – which take it from me if you live in the wild you will – then every rustle and scamper is a harbinger of doom. Mice love to shred things like sacks, polypropylene or otherwise. The only thing they can’t comfortably destroy seems to be metal.
In truth these events are unlikely, especially once you've plastered the house (though mice can and do gnaw through earthplaster). But the bottom line is, if you want your earthbag house to remain solid even if someone slashes the bags open, superadobe is the way to go.
So there you have it. In an earthbag.
Now let's hear your stories. Have you tried filling your bags with something else? Did it work?
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