From Earthship to Earthbags

This is a long overdue post and several external movement have prompted me to finally write it.

A while back I wrote how we moved from hemp construction to Earthships. Well the movement continues and we have moved away from Earthships too. This happened gradually and for numerous reasons:

  1. Expansive Clay Soils – we are proud owners of lots of clay-rich soil which expand when wet and contracts when dry. As I was doing research into Earthships specifically and underground houses generally this seemed to be a problem. Expanding clay soil can place tons of pressure on the walls of a house which can cause it to collapse. So for some time I lived with the question is it possible to build an Earthship in expansive clay soils? My conclusion was that the problems was not the clay soil but moisture.
  2. P.A.H.S – As I did more research I started to come across evidence hinting that Earthships do not work well in our climate (moist and cold). Just recently I came across clear evidence of this. I continued my research and was blown away by an old book called Passive Annual Heat Storage. The book introduced a method by which an underground house is insulated with the soil around it, transforming the surrounding soil into a huge heat battery that charges itself during the warm months of the year and discharges during the cold months. The book confirmed my suspicion that the problem with clay soils is indeed moisture and not clay. The “insulation umbrella” concept described in the book (together with other moisture related strategies) provides a solution to keep the clay soils surrounding the house dry – providing a resounding (even if for now theoretical) answer: yes, underground houses can be built in expansive clay soils by keeping moisture away and in doing so neutralizing the “expansive” quality.
  3. Tires in Romania – we could not find a feasible way to get used tires in Romania.

Empowered by the P.A.H.S knowledge I continued my exploration and started looking into earthbags (it’s a terribly designed and uninviting website but has valuable information). I loved the simplicity and ease-of-construction when compared to ramming tires with earth. I would not have considered it a feasible method of underground construction had it not been for the P.A.H.S. method. I do now.

… and so this is the house that we plan to build.

Of Earth Inside the Earth

The house will be completely buried in the ground except for the south-facing aspect. It’s intended location is on gentle south-facing slope. We will excavate for it into the slope.

Most of its walls will be load-bearing earthbag walls. Hopefully our clay-rich soil (that will be excavated to make space for the house) will provide most of the material needed for the earth-mix that will go into the bags. There is no material more local than earth.

The floor will be an earthen floor and the walls will be covered with earthen finishes.

The roof is an as yet unresolved challenge. It too will be covered with earth and will therefore need to carry a very heavy load (current estimation 1.2 tons per square meter). This weight will probably be supported by round timbers though this is not yet final.


We are planning a house that will be ~200sqm. It is designed to spaciously accommodate a small family. It will have a main part and a smaller, attached living space for additional privacy.

P.A.H.S. – 21 Degrees Celsius All Year Long

Thanks to the P.A.H.S. insulation umbrella the house will (after 2 or 3 years of acclimatization) eventually settle on a steady all year-long temperature of 21c. During the warm/hot months excess heat will be stored in the huge earthen thermal battery. During the cold months heat will be drawn from the thermal batter.

This means that we will not need any additional energy input to keep the house warm. Even the water supply that runs under the insulation umbrella arrives at the house at 21c which means that less energy is needed to heat water.

The temperature of the house is a function of how much heat gets into the house (which depends on how much windows it has) and how much it can store (depends on numerous design factors). It is nearly impossible to change the temperature of the house after has been established. Any attempt to heat it will be futile because the energy will be drawn into the thermal battery surrounding it and you would need to invest a huge amount of energy to change that.

Imagine not having to cut down a single tree for heating!?

Rocket Stoves

We do expect to have at least one rocket stove for comfort … to boost the temperature to 23 -24 degrees when we want to … and to heat water during the months when solar-heated hot water is not available.


ventilation is, we’ve come to believe, an important and often missed aspect. The air in the house should be regularly exchanged. Fortunately the P.A.H.S. strategy includes a passive ventilation system (no fans and no electricity to run it) that brings fresh air into the house all year-long at, you guessed it, 21c. The ventilation system also plays a key role in storing excess heat when it is generated (summer) and retrieving it when it is needed (winter).

The trick (and the one challenge that still worries me) is to build the house air-tight. You should not need to open/close windows in this house ever. During the summer months the passive ventilation system will draw hot air out and store the heat in the thermal battery (instead of letting it escape out windows). During the winter months the passive ventilation system will draw air in from the outside, running it through the thermal battery and bring it up to room temperature.

Imagine fresh air during winter at room temperature (and stale air removed) without losing heat to the cold outside!?

Passive Refrigeration

Michael Reynolds in his classic Earthship books points how ridiculous refrigeration can be: we build boxes to keep the cold out, spend energy to get those boxes warm then build smaller boxes inside and spend more energy to keep those boxes cool.

With a slight change in configuration, the same passive ventilation method that is used to regulate the temperature of the house can be used to create a cool space (let cold air in and warm air out). In the Romanian winter that cool is cold enough not just to refrigerate but also to freeze.

Our intention is to build an insulated (from the warmth of the house) space within the house that will harvest winter coolth. That coolth will be stored in water bottles that will freeze. The space will be divided in two. One part will hold a freezer that will be exposed to the natural freezing temperatures. A second part will hold a refrigerator. Both will be unplugged during the winter months. When spring sets on and the ice melts and there isn’t enough coolth they will be plugged back in and run on electricity (which is once again available as the days get longer and the sun shines through).

Photovoltaic Electricity

We would like to be able to live off-the-electric-grid. The first step towards doing that is by drastically reducing consumption:

  1. The house is naturally heated so that no electricity is needed for heating.
  2. Hot water is pre-heated due to the thermal battery, then heated with an efficient rocket stove during winter and with a solar-hot-water panel in spring/summer. Very little electricity needed for pre-heating small quantities of water.
  3. Refrigeration is designed to work on the naturally available coolth of winter when there is very little sunshine to produce electricity.
  4. Large south-facing windows and a one-room-depth house design provides plenty of natural light all year-long.

This leaves us with some lighting and other smaller electronic devices (computers and such). This should enable a photo-voltaic system that will provide all our needs in summer months and most of our needs in winter months.

Attached Greenhouse

The front of the house will be a large greenhouse that will serve multiple functions:

  1. Harvesting heat during winter months.
  2. Extend the growing season.
  3. Growing plants that can not tolerate the harsh winter (lemons? avocados? even bananas?)
  4. Having a pleasant green space to spend time in during the cold winter months.
  5. Consuming grey-water created in the house (this is much easier for us since we use composting toilets and do not have to deal with black-water).
  6. A transition space between the outside and inside (keeping the inside cleaner).

Rainwater Harvesting

For a long time we were faced with a dilemma:

  1. A standard roof that will harvest rainwater for the house but somewhat compromise insulation (all heat inside the house rises) and durability (all mechanical roofs are prone to deterioration and require maintenance).
  2. A living roof that will provide superior insulation and durability but is practically useless for harvesting rainwater (10-15% of a similarly sized regular roof).

After long deliberation we came up with a solution that will provide us the best of both worlds. The house will be built with a living roof (a relatively massive one) that will complete the insulation umbrella.

We will be building a “mirror” structure of the house slightly uphill. This will be a simpler and cheaper structure. It will include a workshop, storage spaces and an open yet sheltered work space for a summer kitchen and other outdoor activities (some of these functions are now unmet or just temporarily resolved). This second structure will have a metal roof for harvesting rainwater that will be stored in an underground cistern that will supply the main house.


None of these technologies are new. All have been implemented in one way or another. We do not yet know of a house that has been built using all these technologies combined in a climate like ours. It has taken almost 3 years of research by trial and error to reach this formula which has the potential to be an affordable, ecological, sustainable and scalable method of construction.

Scalable is an important quality worth explaining. From what we’ve seen most eco-houses fall into one of two groups. One are small hobbit-hole-like homes which are often the result of do-it-yourself builds with natural materials (these do not scale up very well). The other are large and expensive homes that rely on expensive and complicated technologies to achieve an illusion of sustainability (that often ignores their embodied energy and their technological dependence). We are trying to create something that is in between these two worlds. The P.A.H.S. method can be applied to any size home and it is a core component in the overall efficiency of such a house.

This will hopefully be a very-long-term house.

Evidence That EarthShips Do Not Work in Europe

That title isn’t quite fair because it isn’t exactly true. But given the hype around Earthships I felt it is a deserved.

This short post was prompted by a longer article where the author inquires into the performance of Earthships in Europe. He raises exactly the same questions I encountered in my research. He made an effort to reach out to known Earthship projects in Europe to inquire about their performance and this is what I read between the lines:

  • There are very few Earthships in Europe.
  • Most European Earthships do not have permanent residents (if at all, cats do not count).
  • There is very little information on performance.
  • From what little information there is, it seems there are severe performance issues.
  • There is very little sense of joy from all this.

The author is less blunt then me. I’ve written before that I think the Earthship “formula” is wrong for a cold and moist European climate. I also feel that the knowledge around Earthships is incomplete because I did not come across any information on why they are designed they way they are,why they work where they do and why they do not work in the European climate.

I did however find the Passive Annual Heat Storage book where (1) I finally found explanations on how underground houses behave and (b) answers to all the questions presented in the linked article and then some.

Australian Earthship Build Video

Dan contacted me and sent me this video of an Earthship built in Australia. The video includes image sequences that are packed with information. If I find any more information on this build with still pictures and words I will update this post with it.

Tires Together

One of our core projects here at Bhudeva is building our future house. We have been doing a lot of research on sustainable and ecological construction and we have been facing many challenges in bringing existing knowledge into context for our life here in Romania. Our latest design envisions a mostly underground house that will provide us with a year-long steady temperature of 21c without any energy inputs (neither for cooling in the summer nor for heating in winter). The core of our design is based on the concept of Earthships. At the heart of Earthship construction are massive walls built of tires that are packed full of earth.

So for many months we’ve been looking and asking around about tires here in Romania and this is what we found out:

  • Most tire dealers and repair shops sell some used tires that barely have treads but can still just barely be driven for 15-20 ron a tire (just to be clear – they are sold to people with old cars who can’t afford new tires).
  • Tire dealers are required to “recycly” through the state (represented by licensed operators) a certain amount of tires to offset new tires that they import.
  • The dealers are paid a symbolic 50 ban per tire collected from them.
  • Most of the collected tires are then sold off to different uses . Some are recycled (yey!!) into products such as car mats … however …
  • Many (we suspect most) are sold at a premium of 10-20 ron per tire (purchased in quantities of tens of thousands) to cement manufacturing companies (and their likes) who use them as fuel (boo!!) – it seems that a single tire contains a equivalent of 7.5 liters of oil!
  • We know of at least one giant pile of tires in Cluj-Napoca that is just sitting there slowly decomposing in the sun. We assume that other such piles can be found all over Romania.

Used tires is a waste product we (especially those of us who drive cars) are all responsible for creating. The concept of Earthships (built with earth-packed tires) was born out of recognition that this huge source of waste (available all over the planet) can be put to good use in creating houses (which it would seem are also needed all over the planet). Any recycling of tires requires high energy inputs (often starting with shredding). The thought of all the toxicity released when tires are burned as fuel (a single tire contains a equivalent of 7.5 liters of oil!) is mind-boggling. When used to build Earthships the tires are used as is and because they are completely buried they do not decompose or release any toxic gases (which they do when exposed to the sun).

Whenever we speak to someone in Romania about needing tires we quickly encounter an opportunistic greed. Regardless of the “asking-price-per-tire” we would also need to find a solution to sort through tires and have them brought over to our place which incur additional expenses. All this caused us to rethink about construction with tires – suddenly it seemed that concrete blocks that easily snap together would be much cheaper (and way faster to build with) then working with tires. However we really don’t want to resort to massive construction with concrete … so we scratched our heads and though of you … yes you 🙂

Inspired by the awesome waves of goodness we encountered with the introduction of Cutia Taranului we decided to once again try collaborating with you – our fellow Romanians. Also in the spirit of Cutia Taranului we realized that the best way to get tires would be to go around the existing system rather than through it. It boils down to this … the next time you buy tires we would like to ask that you keep your old tires, don’t leave them to be used opportunistically as fuel.

Now look at your old tires … what do you see? Look closely … you are holding a personal invitation to visit with us at Bhudeva including at least a pleasant conversation, a tour and a tasty cup of herbal tea … and best of all you have become a contributer to a unique experiment in sustainable construction taking place here in Romania.

For our house we are going to need about 2000 tires (though we have other structures planned … so we will try to collect much more). Tires come in different sizes which are indicated with a combination of numbers printed on them. All you need to look at is the first number – the one that has the letter “R” in front of it. We need tires that are labeled as either “R15” or “R16′”. The larger “R16” tires will be used for the base of our walls and the “R15” tires will be used on top of them for most of the wall.

Lastly … since we are talking about garbage 🙂  We are also going to need empty cans, empty wine bottles and used cardboard boxes. So if you are already holding on to tires an invitation to visit Bhudeva then please  hang on to these things you may be tempted to throw out 🙂

Since tires are not often changed this initiative may move a bit slow so … please do spread the word to your family and friends 🙂


Building an Earthship in a Cold Climate? STOP

… and read the book Passive Annual Heat Storage – Improving the Design of Earth Shelters by John Hait.

  • Should Earthships be insulated? Yes (but not in the obvious way it’s being done today).
  • Should Earthship floors be insulated? No.
  • Can an Earthship provide a comfortable (21c) climate using passive means during the winter season in a cold climate? Yes.
  • Can heat be collected and stored during the summer for a winter with very little (mostly cloudy) passive solar gain? Yes.
  • Can an Earthship be properly ventilated without having to sacrifice precious heat? Yes.
  • Are skylights a must? No.
  • Is the corridor wall (introduced systemically in Global Model) Earthships required in cold climate? Not necessarily.
  • Can an Earthsip be built in clay-rich expansive soil? Yes, if the soil kept dry.

When it comes to cold (moist and frozen) climates like ours here in Romania, there are quite a few things that felt, to me, incomplete, missing or even wrong in Earthship design (including the latest and greatest Global Model). To me what was missing most is the lack of explanations of how things work and why they are designed the way they are. I could not find satisfying answers in any of Michael Reynolds’ Earthship books (Earthships have evolved way beyond their description in the original Earthship books) nor online in many of the documented builds and open discussions about Earthships.

Then a few days ago I published this post about ventilation problems in an Earthship and began to compose my thoughts for a follow-up post. The solution seemed to come in the form of earth-tubes. The first resources I came across (pretty much as they were presented in the search results) were:

  •  Wikipedia – which provided basic technical information.
  • The Natural Home – which provided a convincing argument for earth tubes.
  • BuildItSolar – which raised some questions and left me with some doubts.

Luckily I stubbornly pressed through a few more pages of superficial search results and on the 3rd or 4th page found an article by John Hait inaptly titled Umbrella Home. The article blew me away. I ordered the book and couldn’t put it down – I read it word for word in just over a day and will be re-reading many parts of it again.

The book truly lives up to its subtitle “improving the design of earth shelters”. Not only does it open a door to a much deeper understanding of earth-tubes but to do so it introduces a fantastic concept of a large insulating/blanket which surrounds an earth-sheltered house in which earth-tubes can really come to life.

The core idea (backed up by accessible explanations and practical research) is to create an insulated and water-proof blanket that encompasses the house and a large area (~6 meters) around it (which can be achieved with more or less the same amount of insulation materials used for standard wall insulation).

This insulated umbrella creates a large body of earth which is dry and functions as a huge thermal battery attached to the house. The house itself acts as a solar collector to slowly charge the immense thermal battery during summer. Then, during winter that battery slowly discharges heat back into the house.

Earth tubes are used with this umbrella (in a way that could not achieved without the umbrella) to passively generate both ventilation and temperature regulation (cooling & warming) of the house. Because the earth-tubes run through the thermal battery surrounding the house they work as a super-efficient heat exchange system. A passive air-conditioning AND heat-exchange system that is simple and affordable.


As a cherry on top  – imagine running an uninsulated water supply pipe under the umbrella and having water preheated to 21 degress (celsius) during winter  (cold water supply has to be insulated under the umbrella). As someone who washes dishes with freezing-cold water (unless I fire up the wood boiler) I am watering at the mouth at the thought of washing dishes with passively heated (no additional energy expense or effort) warm water. Not to mention energy savings in heating bathing water.

This may cause a problem with Earthships that include rain-water harvesting stored in buried cisterns. The cisterns, if buried close to the house, under the umbrella will become a source of warm water. Cold water would have to be cooled somehow and I don’t know what effects this may have on the stored water. Since we’ve decided to forgo rainwater harvesting and put in a green-roof this is not a problem for us.

If you’ve already built an Earthship in a cold climate and it isn’t functioning as well as you thought it would I believe that at least some of the measures described in the book can be added to your Earthship to make it a much better home.

I don’t recommend trying to implement this from the basic information in the article. I STRONGLY recommend reading the book word for word. It is educating and empowering and fun to read.

I am now (again) heading back to the drawing board to revisit and rethink our house design. I feel I know better now and I am grateful to John Hait for his work and for making it available to others.

Earthships and Ventilation in Cold Climates – Problem?

Ventilation and air quality is one of the last and most problematic issues I’m left with in regard to Earthships in cold climates. Cold climate is what I’ve experienced in a mild Romanian winter which includes snow cover, continuous (many weeks if not months) subzero temperatures and no sunshine (passive solar gain) for two week stretches.

To avoid confusion (as I have encountered it myself in trying to figure out this issue) let me re-iterate: the problem I am trying to outline here is not heat but ventilation – the removal of stale air and it’s replacement with fresh air. There is no question in my mind that no matter how efficient a properly insulated Earthship can be, in our Romanian climate, it will require additional heating. However heat and it’s origin does effect the flow of air throughout the house.

In this post I will try to outline what I’ve been able to figure out so far. The bottom line will be that in cold climates there is a ventilation problem. I hope this post provokes further input and conversation through comments. I would especially love to hear from people who have lived in Earthships in cold climates and their experience of ventilation and air-quality. Then, in a separate follow-up post I will try to present what seems to me like a potential passive, energy efficient ventilation solution.

Classic Earthship

The classic Earthship ventilation theory is simple and straightforward. Fresh cool air enters from the operable windows on the front face. This air is heated by solar gain, warm air rises and escapes from the skylight resulting in a continuous flow of fresh air through the living space.

The ventilation problem is already present in this simple model. What happens when it’s so cold that operables and skylights (both covered by snow) are kept close to keep heat in (and snow out). To my understanding there is no air flow.

 The only way to get fresh air in and stale air out is to let the cold in. Earthship theory would say that is not a problem because the thermal mass of the house contains enough warmth to compensate for coolth that comes in through the openings. In our climate I don’t think will hold true. I think we will have to heat the house in addition to water solar gain (hopefully much less then a house built above ground) and ventilating would entail precious heat loss.

Global Model Earthships

The Global Modal Earthships make two distinct changes to the elements of ventilation (actually there is a 3rd which I will address separately, see earth-tubes below). The first is the introduction of the corridor wall which separates the living spaces from the greenhouse. The second is the skylight over the greenhouse which comes INSTEAD of a skylight in each living space (I wasn’t sure about this until I encountered this video from Earthship Biotecture). In this configuration the greenhouse has been described as an air-lock that supposedly provides better climatic control by isolating and containing variations between it and the living space.

 There are now two ventilation circuits in the house. The first is between the outside and the greenhouse and the second between the greenhouse and the living spaces. The ventilation loop between the outside and the greenhouse is obvious and is similar to the classic Earthship approach.

I have some doubts how well the ventilation loop between the greenhouse and living space will work. As I understand it, if passive solar gain is the main source of heat then the greenhouse will always be warmer then the living space. This means that there may not be much flow from within the living space (cooler and heavier air) to the greenhouse (the already warmer and lighter air). It seems to me that the flow in the greenhouse may over-power the flow from within the room. This may be effected/controlled by alternating openings (eg: first ventilating the greenhouse, then closing it and ventilating the living spaces) and height positioning of the ventilation passages between the corridor and living spaces.

As with the classic greenhouse I do not see any potential for passive ventilation on cold cloudy winter days.

When a source of heat is added inside the living space and the hot inside it becomes warmer then the greenhouse – there can be a ventilating flow between the two spaces (and of course heat will be lost from the living space to the greenhouse).

If, in addition to the heat source, the front operables and skylight are opened then there may be some draw of fresh air from the greenhouse to the living space (and of course heat will be lost from the living space to the greenhouse and then quickly to the outside).

So, it seems that any ventilation will come at the expense of precious heat.


Global model Earthships introduce another element they call “Cooling Tubes”. These are tubes that are buried in the ground (~20 feet) behind the house and penetrate the rear wall.

They are intended to provide natural cooling. Warm air in the greenhouse is released through the skylight this creates a draw pulled in through the cooling-tubes. Warm air is drawn into the tubes from the outside, loses heat to the ground in which the tubes are buried and arrives cooler into the house.

This solution addresses ventilation in a hot climate, it does not address ventilation in a cold climate. However, I do believe it points in the right direction. More on that in an upcoming post.

Is It Possible to Build an Earthship in Moist, Freezing, Expansive Clay Soil?

We have beautiful, heavy, clay-rich soil. It’s great for cob (which explains the local proliferation of cob houses), great for earthen plasters and earthen floors but it seems to pose some challenges when it comes to underground construction such as Earthships. I hope in this post to outlines the challenges and what solutions I have come across to deal with if. If you’ve built in an Earthship with such soil then please stop by and share your experience with it. Midway into writing/editing this post I came across this thorough description of expansive soil and their potentially adverse effects on construction. From reading it and a few others resources I feel is it important to note that:

  • Almost all mentions of expasive soil issues are in relation to foundations. An Earthship has no foundations.
  • Almost all mentions of expensive soil relate to hard-concrete responding to intense uneven pressures. An Earthship is inherently a “softer” structure (then concrete) embedded in the earth. We intend to embrace that concept and even our floor will be a “soft” earthen floor and not a rigid concrete slab.
  • Expansive soils are not inherently a problem – fluctuations in their moisture content is a big problem. If moisture content is stabilized then the problem is largely diminished.
  • An Earthship is inherently a massive structure (even more so with a living roof we intend to add) and as such an Earthship is capable of “pushing back” against the forces of surrounding expansive soils.

In addition to all this we have had an opportunity to observe how things behave in real life which is an excellent teacher – especially as I am about to get into a lot of theoretical ideas. We live in a cob house that was built in 1934 and it is structurally sound. It has partial peripheral stone foundations and is holding up find sitting on expansive clay. Other houses in the village were built with without any foundations and have been standing for many years. Of course there are also decayed houses … but I cannot say what kind of role soil-expansion had to play in their history. Though they have not yet withstood the test of time, we have built two underground concrete boxes (with manhole access) for our water infrastructure. Their walls are ~10cm thick with rebar – and they have shown no signs of stress problems. We have had a few ditches open over recent months and they have seen many transitions from wet to dry and they also showed no structural decay.

Expansive Clay Soil

It took me time to understand what all the structural fuss and warnings are about “Expansive Clay Soil” and it all went back to understanding the structural qualities of the soil itself. The soil composition itself is considered clay-rich and my first misconception was that that meant it was mostly clay. This is incorrect … clay rich soil has a relatively small percentage of clay particles in it – typically ranging from 10% to 25%. While the clay is not a major quantitative element it is a dominant qualitative one.

Clay particles in clay-rich soil expand when they come in contact with water. As it absorbs water it becomes sealed and much less penetrable for water. This makes saturated clay-rich soil slow-percolating. We witnessed this clearly when we dug a small hole in the ground and filled it with water. The small pool stayed in place for quite some time, percolating into the ground very slowly.

This makes clay-soil a structural force to deal with when building an underground house. There are two phenomena that lend a hand to the expansive behavior of clay. The first was mentioned above – clay absorbs moisture and expands. So, for example, the fall season rains saturate the soil and the clay expands. Then winter brings into play the second phenomena – freezing. The saturated and already expanded clay soil is now exposed to freezing temperatures which cause even more expansion.

These forces are insignificant in a bucket of clay but can translate into potentially thousands of tons of force pushing up against a house that is buried in the ground. After carefully internalizing the “expansive” behavior of clay it seems to me that the problem is not the clay rich soil itself but it’s exposure to moisture.If it’s kept dry then clay rich soil is actually an excellent structural soil – it dries into a very solid earth – ideal for rammed earth tires … IF you keep it dry.

Implications for Earthships

I can identify numerous implications of working with/in rich-clay-soil when it comes to Earthships:

  • Construction work – wet clay soil becomes a heavy muddy substance very difficult to get around in let alone to work with.
  • Rammed Earth Tires – if a tire is packed with clay earth that is not dry (enough?) then when it will dry it out the earth in it will get compacted some more. That could be a structural nightmare.
  • Drainage – clay rich soil has no drainage – it saturates with water and seals itself. Period. Though I haven’t seen this acknowledged in any written materials (off and online) my impression is that that is actually a welcome feature to one half of the water drainage problem of a house – surface water (once the soil is saturated) will simply flow away – so all you have to do is divert it to make sure it flows where you want it to go (preferably away from the house). The other half of the water drainage problem comes from below … and that problem isn’t unique to clay-rich-soil. It simply means that you need to have good drainage beneath the floor and around the house.
  • Structural Pressure – now we that we have figured out that the earth around the house may be pushing up against the house with tremendous force – something needs to be done about it.
  • Insulation – wet earth sucks warmth out of the house. The Earthship is bermed with earth all around and so to maintain energy efficiency any contact with wet earth must be avoided or mitigated.

Possible Solutions

Tire Walls Inherit Strength

In a typical underground house the forces of the soil would be acting directly on standard earth-proofed walls (usually concrete). The first main difference about Earthships is that the walls are massive … twice the width of typical walls. The tightly packed tires offer much more structural resistance then their counterpart typical walls. In addition we are planning to have the internal walls also be tire walls for additional mass and structural support.  In addition, outer Earthship tire walls are designed to lean back into the surrounding earth which offers even more lateral strength. 

Use Dry Clay Soil

This is easier said then done (at least in the Romanian climate which can rain any time and for any duration of time):

  • The building site would have to be setup with a large area which is arranged to dry soil.
  • This area would have to be sheltered from the rain.
  • It would also need to have exposure to sun and open-air circulation to promote drying.
  • It would need to have a large surface area so that a substantial quantity of soil can be dried sufficiently for use in both tires (slow and continuous consumption of soil over a long period of time) and backfilling (rapid consumption of soil in a very short period of time).

I suppose that if the excavated earth was placed in a narrow (north-south) and long (east-west) mound and that if that mound was covered with a slightly elevated clear plastic cover while enabling comfortable access for both wheelbarrows and a tractor – that soil could be reasonably dried!?

This also means that the tire walls themselves need to be kept dry throughout the project. Since Romanian weather includes rain-showers throughout most of the year (except of course in the subzero temperatures of winter) – this means that there need to be plenty of cover materials on site and a quick response when rain showers do appear.

Bring in Alternate Soil

Though it can become a substantial expense it is possible to bring in sandy, good draining soil for both ramming tired and backfilling. The supply of soil can be regulated as needed so it can be kept reasonably dry. Also, since it doesn’t suffer from expansion it would be OK to use it when moist knowing it will eventually dry out.

This is something I would prefer to avoid because (a) it is costly and (b) it goes against the core idea of using local materials for construction.


The design of the Global Model Earthship introduces a perimeter wall of insulation and moisture barrier set about 1 meter away from the outside of the tire walls. This creates two distinct backfill areas: (1) between the tire walls and the insulation; (2) outside the insulation and moisture barrier. The first backfill area between the tire wall and insulation/moisture barrier is a space that can and I believe should be completely covered by a moisture barrier. This means that this soil humidity is going to be relatively stable. If it is filled with mostly dry soil then it will also not change much, if it is filled with moist soil – then it may shrink as the envelope of the house dries over the first years of operation. Either way that part of the backfill is relatively stable and becomes and extends the fabric of the house. To my understanding it should absorb most of the additional pressures that come from the surrounding soil BECAUSE it isn’t structurally packed liked the tires – it is a more dynamic wall up against the more static tire-wall. Then there is the second – outer backfill – the one that is outside the moisture barrier. For this backfill I would prefer to use a good draining soil. It is a smaller volume of backfill and therefore less expensive to do so. It would serve two purposes. One is faster draining of any moisture that comes near the fabric of the house. The other is an additional pillow against the pressures of the surrounding earth. So already there is plenty of support against the potential pressure of the surrounding expansive clay soil.


I am thinking of starting the build by placing (on the excavated undisturbed soil) ~30cm of gravel (with built in drainage – see below). My thoughts are to excavate in such a way that the resulting surface will be slightly downhill (more elevated towards the back of the house. A level layer of gravel would then be placed on it. The gravel would cover the entire construction area up to and including the perimeter insulation wall and future tire walls (which will be built on the layer of gravel).

Common sense tells me that the gravel layer may also act as a flexible absorption layer should their be any excess pressure due to expansive soil from below.


On the gravel I would place a french-drain system made up of:

  1. A perimeter drain pipe.
  2. An inverted U drain pipe in every U module – with a T joint which leads out of the U and into the greenhouse/corridor (I feel it is better to avoid running any pipes under the tire walls). The  corridor connections would need to eventually pass through the stem wall of the inner corridor wall.
  3. Two main main drain pipes which collect flow from the U-drains and lead out to the two sides of the house and connect to the perimeter drain.

This would both remove excess moisture should it ever accumulate and create (as our architect suggested) a pleasant and mud-free work zone.

Living Roof

Our intentions are to install a living roof instead of a rain-collecting roof. The weight of the living roof as carried by the all the (inner and outer) structural tire walls is an additional counterweight to pressures from the surround soils. Most of the weight of the roof will be transferred down into the ground below the house. Some of the weight will be transferred to the side walls to do their outward leaning angle. This is unexpected and welcome benefit of the living roof.

Moisture Barriers

Moisture barriers are, I believe, a given in Earthship design (and any other well designed overground/underground house). Though in an Earthship I believe there are two aspects to this challenge. One is during construction (which in a self-build can take years) and the other is the typical finished house. My thinking is to start with the moisture barrier from within the tire walls – so it would be placed on top of the gravel. I think that a 4 meter wide would sheet would be enough to go from within the wall, underneath the tires & the the inner backfill and over the top of the first layer of insulation panels. Then each course of insulation would be covered by another overlapping sheet. In the end a top sheet of moisture barrier will extend from the roof and will overlap the top course of insulation sheathing. During construction a temporary cover will be needed to cover the breadth of the tire-walls + infill area + insulation panels. The floor area can remain uncovered as rain water will be diverted by the drains.


Though insulation is not directly related to the structural aspects of expansive soils it can effect the thermal performance of the house within these soils. Expansive soils hold a lot of moisture content and wet-earth can suck warmth from a house much more then dry earth.

Thorough insulation (as would be required in the Romanian climate), in my opinion, has not yet been achieved in Earthship designs (based on freely available information online). This is a testament to the fact that Earthships do not originate in cold and soggy climates and soils. Insulation was added in later Earthship designs and is now standard in the Global Model, but I believe it is still not up to the task of dealing efficiently with the Romanian climate. First, as designed in the Global Model, the insulation panels are better off protected from moisture – so it is sensible to install them within the moisture barrier sheath. In addition to that I would like to extend the insulation to close off additional energy bleeds from the house:

  • Floor insulation will be added throughout the house – above the gravel drainage layer and beneath the earth floor.
  • Floor insulation will also extend beneath the tire walls – it will be laid out around the perimeter and beneath the inside walls before tires are put in place and filled with dirt.
  • Floor insulation will also extend beneath the inner backfill area and through to the perimeter insulation panels.
  • The stem-wall for the inner corridor wall will also be insulated beneath ground level with R5 insulation panels to prevent energy bleed through the concrete.
  • Similarly the concrete footers for the front wall (living roof load bearing) posts will be insulated below ground.
  • Roof insulation will continue and meet the perimeter insulation panels using R10 panels (this insulation is closer to ground-level and therefore exposed to more sever ground-frost).
  • On the front face wall frost-blocking (45 degrees) insulation panels will be installed.

I am still debating what to do with the planters. I believe that the presence of composting soil and living plants and solar gain makes adding ground insulation in the planters redundant … we’ll see. Together with the bermed earth and living roof this should provide an effective shell of insulation that should prevent energy bleeds from the core of the house to the surrounding earth.


It seems to me that if properly dried soil (still no clear idea on how to achieve this) can be created and maintained on the work site, together with uncompromising moisture barriers and insulation should make it OK to build an Earthship in clay soils. I would be grateful to hear other opinions and other experience on this issue.