House Ideas for Hard Clay & Rock?

Scenario: You have just acquired the following property:
Zone 7
Very heavy clay with some silt, riddled with rocks of all sizes
Undulating land full of hills and draws running N/S
Machine-compacted areas are extremely hard and riddled with dime to basketball sized stones

This house will have to pass through hot, humid summers without air conditioning.

Challenge:  Choose a long-lasting building method using as few imported materials as possible.  

Hey kaye, hope you are well.
You site sounds interesting although i dont have a massive understanding of The usda zones.
Have you found much information to help with your situation?
We have a plot (I think zone 10a, but it's outside of the USA) that has hard clay and rocks on a sloped site.
We at leaning heavily towards stone foundations, mud brick walls and a large wooden roof frame/metal roofing.
Our area is dry in winter and wet in summer with relatively  low humidity all year. So our designs should differ a bit however perhaps our materials may not.
Given the cost of sand (for mud bricks), building with what we have makes the most sense and also makes use of the material needed to be removed for the house with.
Love to hear how you get on with your decisions. Good luck.

We've researched cob, straw bale, and earthbags.  I don't like the cost and transport involved with straw, and cob would take FOREVER. Overall, earthbags would require less imported materials than the other two methods on our site, and less time than cob.
So...at the moment, I'm considering an Oehler-style earthbag compound structure.  Dug into the hillside, rubble trench foundation, sloped roof diverting rain water further down the hill, and a shady terraced garden view.  We could probably put some cob on top of the earthbags to make direct contact with the roof beams, which will be slanted.  If we can play well with water and shade, we may be able to put rocks and flowing water from the root cellar in the terraced area to act as a natural air conditioning.  It would have to then be diverted away from the walls, though.

Sounds interesting. What sort of plants and animals do you have around there?
Seems to me that the cheapest way to build is with what you have. Design and engineering can be a hassle and take time as you mentioned but can save alot.
Earth bags are the woven plastic bags/tubes the are filled and smashed right?

jesse dylan wrote:Sounds interesting. What sort of plants and animals do you have around there?
Seems to me that the cheapest way to build is with what you have. Design and engineering can be a hassle and take time as you mentioned but can save alot.
Earth bags are the woven plastic bags/tubes the are filled and smashed right?

The area tends to have cattle, chickens, some goats and sheep.  Every now and then you'll see the special fellow with some alpacas, horses, or mules.
Plants include timber like oak and chestnut, hay, snap beans...any cool season crops generally succumb to the hot, humid summers by the end of May.  Being in the hills, Monsanto hasn't gotten to much of a grip on the area, but they are right next door (north east), where the land is flat and the soil is deep.

"Woven bags/tubes"...Pretty much!  Hopefully the HUGE amount of rockiness in the land will help avoid too much clay in the bags.  I've been looking into tube sandbags.  I figure that will make it stronger and save time.

Hey-a,
There is a friend i know who teaches how to make  buildings with these earth bags. When I first saw his place ( mountain side with clay and rocks) I questioned myself as to why bring in other materials and have these limitations to design.
Once I knew him a bit better he told me that a lot of it was that he loved the technique and what it represented. Now, he continues to teach the technique but it's unlikely it will be used for more structures on that site.
I'd consider what you have and why you are leaning towards the bags.
A site I am designing with my partner has not got any 'GMO' crops as such but there is pesticides and groty fertilisers everywhere, sprayed from planes also. Big business has got its hooks in every which way.
Cheers

Fortunately we don't have the pesticides and fertilizers on the area--it's really just recently logged semi-wild, rural land with road access.  Forests, hills, clay, rock.  Little yellow finches flitting about, singing their song.

Are you saying that clay and rock is a bad situation for earthbag construction?  Or do you think there is an even better method?  If so, what is it?  

I was leaning toward the bags because my impression was that it would be faster and maybe cheaper than cob, if we could simply fill the bags with our local soil.  Also, I like the idea of the extra barrier the bags provide to protect against water.

I appreciate your input and thoughts greatly!  

Hey-a, sounds like you have a nice spot there.
There are a few reasons i would be cautious or even reconsider earth bags. Although I am by no means not an expert.
As a water barrier I have not seem then work well. They absolutely have to be covered from the elements.
Covering can be tricky due to many things such as :
Trapped  moisture in the soils,
Settling (changing shape has greater impact on something monolithic such as a 'dome'
proper ventilation, if a dome utilising space efficiently and so on.

I assume that you are familiar with the benefits of earth bag so I won't make an incomplete list as I did above.
I suppose it is really a matter of if it is the most suitable.
If you have currently have most of the materials and you lack time/human power maybe look for some helping bee, wooffers, or something of The like.
I do believe that sand bang construction is an important and useful technology.
In the right situation it could be the best option.
Seems soil mix is pretty important for a well made long lasting building.
Let me know how you get on with it.
Cheers

The actual cob work would be a major project, but it sounds like you could excavate and make the walls from the material right on the spot, not more than a few feet of transportation. The only thing you would need to import is straw, and maybe some sand if the mix is not sandy enough to minimize shrinkage. Gravel in the mix will help there, though if it is anything like the glacial till dropped directly by the glacier that I have, it will not be amenable to stomping or mixing by bare foot or hand - too much sharp material.

If you have plenty of rocks, you may be able to make a good rubble trench foundation, and stone walls to above grade on the high side, then transition to cob.

If you have oak and chestnut on your land, building a frame from that and infilling with light straw-clay might be a good direction. Do you have any woodworking experience?

Hi all,

I've attached a few photos I found that look a LOT like what we have out there.

While there is some timber on the property, we do not have woodworking or construction experience--another reason we are clinging to the idea of earthbags or something similar...we have heard they are "idiot-proof." O_O  Due to the fact that we want a heavy load of earth on the roof, building a safe, stable, load-bearing structure is paramount.

I did not mean to suggest that we were planning to leave the earthbags exposed to the elements--we were hoping to cover with cob plaster and tadelakt/lime plaster.  We would also have a huge roof overhang.

If we had to import sand for cob anyway, plus spend all that time filtering out those millions of rocks, mixing, stomping, forming, and slapping, why not just bring in the sand and stuff the bags with sand+local mix?  I'm just trying to save unnecessary labor.

The local ground is SO compact and hard where the machines were driven over it, it really makes me think there has got to be a good way to convert this ability into a construction method.

If that is really what your material looks like, it appears to be primary clay from decomposed granite (or something similar). I would think there would be no more treatment needed for cob than for earthbag filling. Before assuming that you need to import sand, I suggest trying a small batch of the material straight with straw, only picking out the rocks that make it too hard to handle (>golf ball or >tennis ball, depending on your attitude), mixing it in a wheelbarrow with a hoe or similar method, and forming a block of cob. Measure it (scratch lines 10" apart) when wet and see how much it shrinks when fully dry, and how it generally behaves. Pick at it to see how strong it is. Maybe you will find that the natural aggregate makes fine cob all by itself. Obviously for surface layers you will have to refine the material, but that will be the same no matter what construction method you use.

We have a lot of chet on the surface, and the environmental experts told us there is a lot of limestone in the area.

I'm excited to try those tests.  Can't wait to get out there and get my hands dirty!

Do a lot of rocks affect the integrity of cob?  It would inevitably be riddled with stones.  My dream roof is heavy, with heavy timber covered in feet of earth, so I need as much load-bearing help as possible in my walls.

Con or mud brick if done right will have no problems supporting a green roof.
A simple rectangle frame of wood or metal with a metal mesh screen should help.
As long as the holes in the screen are the size of the stones you wish to include.
It's alot easier with dry material. It also means you can make your mix the same every time. That is you can add the water to the dry mixture and control the moister content.
The earth bag way requires more work if you only have two or three people I would say. A bit more stuffing around.

Kaye Harris wrote:We have a lot of chet on the surface, and the environmental experts told us there is a lot of limestone in the area.

Just what I thought when I saw the pictures. Not weathered granite, that's ocean floor stuff. Can't remember the name but you may need both a filter and water softener system.

Here is an example of earth bag with cool tube air conditioning in an environment like yours but with more trees.

Something you might try is to dig out a fresh sample of your earth that way it has not had as much time to oxidize. Then mix in some water glass until it has the consistency of wet concrete. Mix it for at least two minutes and put it in a butter tub or some closed container-- flexible one to aid in releasing. Set it out in the sun and see what it looks like after 24 hours. You can do a few samples from different parts of your land.

If any of the samples set hard then take them out of the tubs and wait a week then boil them for 15 minutes. If they stay hard you have a winner.

You can make your own water glass with crushed glass bottles or sand mixed with ten parts water to 4 parts lye. This mixture will get very hot and is very danderous so goggles and gloves and heat proof container until the heat reaction has finished then you can transfer to plastic. Stir a few times a day when you get a baume reading of 40 you can test if it is a good batch. I think we had better luck with sand. Or you can buy it but not all are equal. One made for geopolymers will always work. The others would need a test batch.

If nothing sets then you can add 5-20% calcined clay and try again. This material is breathable unlike Portland based concrete.

Good luck whatever you end up using

I've done a tiny bit of building with earth bags and a good amount with cob. It's a tough choice but I decided to build my small house with cob for these reasons:

-I am using my tractor to mix the cob so I can mix a huge amount of cob super fast even by myself (I'll put out a video soon of how I do it but there is some info out there already on the technique)

-Cob walls are built monolithicly so they are one big peice making them exceptionally strong

-I prefer the process of building with cob because I can design as I build, meaning, I can choose custom angles of walls, build shelves, seats, built in bed frames, etc. I find earth bags limiting in those aspects and require more planning ahead.

-Cob is so pleasent to build with. I find smashing the earth in bags less comfortable and more repetative.

-Rocks can be integrated into walls to use less cob and save time.

Hope some of this helps. I agree with doing tests first.

I think , Kaye, the first action is to get two things started as PRE-conditioning on the soil. As much mulch as possible (keeps a bit of moisture in the soil and allows that hard soil to soften-slightly). And perhaps throw down a cover crop that will break up the soil and loosen the rocks, such as daikon radish. Not really intended to harvest, but intended to leave in the soil. When you are ready to actually grow other things , you will need to mow or cut the tops off, let the radishes rot in the ground and it will break up that clay and loosen rocks for you. The following year (or if you are really industrious, maybe the same year) plant a few trees that , again will start to break up hard clay with their roots, perhaps nitrogen fixers to add to the soil and begin to provide tiny bits of shade to keep the soil softer.  After a few years of mulching, cover cropping and tree growth, you may be able to describe quite a different soil condition. I would leave most rocks there unless it is just not possible. Then use the rocks you take out to create rock features that allow you to plant plants behind them for wind protection or...add soil over a pile of rocks and plants IN them for  plants that need a drier root area (like Mediterranean type plants-olives or citrus) It is ALWAYS in the preparation. The more thoughtful planning and prep, the easier the task later.

Congratulations on finding a piece of paradise!  I think your oehler style house drawing is great and will provide the cool you need for the long ozark hot season, particularly if you can plan for air movement (suck air in from a shady location using a solar chimney, for example) but also remember you are blessed to have lots of sun during the shorter cold season there.  with proper passive solar design (mostly sizing and overhang design of south facing windows)  you can reduce your winter heating load to practically zero.  Something like 35 percent of your south wall in glazing, or equivalent, but with an overhang that will keep that glazing shaded totally for the hottest months, partially for the months where you need some heat, and totally in the sun during the coldest months. there are online tools that will tell you about sun angles at different times for your location.  I like this one
http://aa.usno.navy.mil/data/docs/AltAz.php
you can often get your hands on failed thermal panes as a cheap option for windows, or do as i did and make your own cheap double pane windows from clear acrylic (plexiglas).  if you drill little holes in two diagonally opposed corners of a failed thermal pane in the outside pane the fog will go away. this will take some care so as not to break the glass, but there are glass drilling bits out there that will allow you to do this.

also with your high clay content, land contours and road access it seems you may have great potential for major water impoundments.  A little well planned earthworks early on can get you more than enough water storage to meet all your irrigation needs during the hot dry spells and generally keep your growing spaces hydrated.  also consider diversion trenches upslope of your house to DEhydrate all the soil in the vicinity of your house.

Also be sure to do your research about structural stability of earthbags.  A bond beam might be a good idea (a structural beam along the top perimeter of walls- could be just logs or other wooden beams strapped together)  then your rafters will sit on top.  the bond beam ties the roof to the walls as a whole.  Also the walls will have some kind of wire holding courses of bags together.  Earth bag walls plus sod roof adds up to a lot of weight, so its serious business to get it right structurally but totally possible, even just following a do it yourself book.

I was thinking about this today after my last post and wondered about building using rammed earth. Might be a compromise between cob and earth bags. Not too hard to build, good forms and a backhoe and some sort of compactor.

Kaye Harris wrote:We've researched cob, straw bale, and earthbags.  I don't like the cost and transport involved with straw, and cob would take FOREVER. Overall, earthbags would require less imported materials than the other two methods on our site, and less time than cob.
So...at the moment, I'm considering an Oehler-style earthbag compound structure.  Dug into the hillside, rubble trench foundation, sloped roof diverting rain water further down the hill, and a shady terraced garden view.  We could probably put some cob on top of the earthbags to make direct contact with the roof beams, which will be slanted.  If we can play well with water and shade, we may be able to put rocks and flowing water from the root cellar in the terraced area to act as a natural air conditioning.  It would have to then be diverted away from the walls, though.

I'm new and not sure how to reply but here goes, live in AZ, and I love the earth bag homes! I have so many of my own ideas that started flowing after I watched YouTube videos. They are amazing and easy to build! This is my plan if I ever find some land.

Jason Learned wrote:I was thinking about this today after my last post and wondered about building using rammed earth. Might be a compromise between cob and earth bags. Not too hard to build, good forms and a backhoe and some sort of compactor.

LOL. That's just what I was about to post, but Jason beat me to it.
Dr. David Suzuki did a show about alternatives for the future and he visited a rock stars home made of rammed earth. You can do some neat things with that as well.

Let me add another recommendation for rammed earth. Faster than cob, Much stronger than earth bag, and by your description of the compacted dirt on your land you have good material at your feet.

You speak of having a heavy roof - rammed earth has tremendous compression strength to hold up that roof, approaching concrete and much better than earthbags.

Thank you everyone for all the replies!  This is getting juicy.

We won't have access to a backhoe, but we will have a gas-powered rototiller.  I have heard this makes mixing cob 5 times faster than usual.  The lack of serious equipment is another reason efficiency is important.

I did research on rammed earth, and it seemed like you needed a lot of special imported clays and sand to essentially make smooth sandstone.  Could I really take what I have (adding the right amount of sand) and just pound it into a frame, stones and all?  That would save a lot of time, but it seems too good to be true.  Also, don't you need a typical foundation for RE?  I would really like to do a gravel drain plain/rammed earth floor as I do not want concrete.

Regardless of method, I was imagining transitioning to cob at the top to make to help make a smooth slope for the slanted roof.  I figured I could also put the wood beams into that cob topping to hold them in place.

Kaye Harris wrote:
I did research on rammed earth, and it seemed like you needed a lot of special imported clays and sand to essentially make smooth sandstone.  Could I really take what I have (adding the right amount of sand) and just pound it into a frame, stones and all?  That would save a lot of time, but it seems too good to be true.  Also, don't you need a typical foundation for RE?  I would really like to do a gravel drain plain/rammed earth floor as I do not want concrete.
.

You could always make a small form and ram it with the head of a sledge hammer and then de-mold it and see how it looks.

Also I really like using chemistry, you could throw some ash from your fires in the mix with a little water and see if it changes the rammed earth's performance. I think we used a shovel full or two for a cement mixer load of thermal cob just to see what would happen and that section of cob was rock hard in an hour or two but the rest of the area was still soft. If you try it and it does not make a difference then no harm no foul. If you try it and it does, please post a picture. I was silly to not take a picture of mine until it was too late.

Jason

Here is a cob brick basically done as rammed earth that this is the third winter of sitting out continuously in the weather.   The only concession has been putting a stick under one end of it so that top isn't flat and can drain off.  Otherwise it has been sitting on the same log for nearly 3 years exposed to the weather.  It was one part clay, 3 parts coarse sand with the reinforcing fiber being baler net wrap instead of straw.  The thinking being that natural fibers provided a path for moisture to get in while the plastic doesn't.  It was beaten into shape so probably nearly to rammed earth standards.  Roughly the size of a house brick but just slightly longer.   I can put a support under each end and stand a 250 lb man on the middle without breaking it.  If it was a continuous wall with a roof over it and where buried moisture protection things are looking good.  While this is a good clean clay it is nothing special.  If fired it survives a bisque firing but melts it you try to high fire it.  So nothing special there.   It is nearly waterproof with no organic in it.  As for the sand it is just coarse gray river sand with a fairly angular nature.  Washed the debris out of the clay and the fine sand, silt and clay out of the other so I knew what I was dealing with and could reproduce it.