Cob, earthbag or straw bale? Which is best?

We live in Alabama where we mainly have hot and humid weather with maybe 2-3 months of chilly weather around the 20s or 30s, give or take. We rarely have snow but freak occurrences do happen and we get about 57" of rain annually.

Our budget is tight (under $1,000) and our timeline is short (2-3 months max).

We dug down about 1.5 ft and did a jar test (see image) but I don't know if we did it right and if we did, I'm not sure if we have decent site soil to build with. Thoughts? If we don't, what kind of clay and sand do we need to buy? How many tons of each for a 200-300 sq ft house with 8' tall walls on the front and 6' tall walls on the back?

Do we need a rubble trench or can we build the house on an above ground foundation such as a deck? If a trench is best, what kind of gravel and pipe do you all recommend? Is a 1/4" drop per ft good enough for the slope?

Any and all advice is greatly appreciated!

I live in ohio.  People have tried cob here.  It's fun to watch it melt slowly over the years because of the moisture here.  Cob, like its sister Adobe are meant for dry conditions.  Even soil cement, which I experimented with,  melts here and it probably would in other wet climates.  Cob is ok for indoors here though. I thinki straw bale might be similar because it usually has a breathable cob exterior. How's your supply of pallets?

With that budget,I would use tires.
I would cut off the sidewalls,lay them out, fill with soil, ,compact with shovel,stack the next course,repeat.
Build a scrap lumber and discarded plastic roof, topped with used carpet to protect the plastic from UV  exposure
Screw layers of cardboard and plastic to the tires, inside and out. Finish with pallet wood.
Potentially only need to buy an impact driver,bit, screws and shovel.

Cob Cottage Company is based in Coquille Oregon which gets an annual 55" of rainfall each year and their buildings are in perfect condition. Cob is more than suited for wet weather you just have to protect them adequately. Get the "hand sculpted house" by Ianto Evans or "The Cob Builders Handbook" by Becky Bee; i've put both links below. You need to have a good "hat and boots" which means build up your water impermeable stemwall well above the ground and make nice big overhangs for your roof, think 2-3 feet.

https://www.amazon.com/Hand-Sculpted-House-Practical-Philosophical-Building/dp/1890132349/ref=sr_1_1?ie=UTF8&qid=1527609526&sr=8-1&keywords=cob+house

https://www.amazon.com/Cob-Builders-Handbook-Hand-Sculpt-Your/dp/0965908208/ref=pd_sim_14_2?_encoding=UTF8&pd_rd_i=0965908208&pd_rd_r=39DJZ1QHAZFRBPF56TXE&pd_rd_w=1Kj6g&pd_rd_wg=Ab2Dl&psc=1&refRID=39DJZ1QHAZFRBPF56TXE

Cob will be too heavy for a platform build house, you need a rubble trench foundation and that will definitely help with drainage. Again, I highly recommend the books mentioned as they outline all the questions you might possibly have about cob. 3 months is short, but doable if your design is 200-400sq feet. Get some friends together for a building party. I would recommend building with strawbales just for speed. You could stack all your walls in a week. The gravel for rubble trench can be anything, sharp gravel needs much more compaction than round drain rock.

Make a few test cobs--like brick size--with the soil you have and see how it fairs to dropping on the ground. As for tons, do the math for volume with your walls. 7' average wall height at 2' thick with a run of 70' of wall is 980 cubic feet of material. That is about 35 yards of material at 1 ton each.  This answer was brought to you by the really rough estimate organization, where we estimate things that cannot be properly determined from my work computer.

Daniel Ray wrote:Cob Cottage Company is based in Coquille Oregon which gets an annual 55" of rainfall each year and their buildings are in perfect condition. Cob is more than suited for wet weather you just have to protect them adequately. Get the "hand sculpted house" by Ianto Evans or "The Cob Builders Handbook" by Becky Bee; i've put both links below. You need to have a good "hat and boots" which means build up your water impermeable stemwall well above the ground and make nice big overhangs for your roof, think 2-3 feet.

https://www.amazon.com/Hand-Sculpted-House-Practical-Philosophical-Building/dp/1890132349/ref=sr_1_1?ie=UTF8&qid=1527609526&sr=8-1&keywords=cob+house

https://www.amazon.com/Cob-Builders-Handbook-Hand-Sculpt-Your/dp/0965908208/ref=pd_sim_14_2?_encoding=UTF8&pd_rd_i=0965908208&pd_rd_r=39DJZ1QHAZFRBPF56TXE&pd_rd_w=1Kj6g&pd_rd_wg=Ab2Dl&psc=1&refRID=39DJZ1QHAZFRBPF56TXE

Cob will be too heavy for a platform build house, you need a rubble trench foundation and that will definitely help with drainage. Again, I highly recommend the books mentioned as they outline all the questions you might possibly have about cob. 3 months is short, but doable if your design is 200-400sq feet. Get some friends together for a building party. I would recommend building with strawbales just for speed. You could stack all your walls in a week. The gravel for rubble trench can be anything, sharp gravel needs much more compaction than round drain rock.

Make a few test cobs--like brick size--with the soil you have and see how it fairs to dropping on the ground. As for tons, do the math for volume with your walls. 7' average wall height at 2' thick with a run of 70' of wall is 980 cubic feet of material. That is about 35 yards of material at 1 ton each.  This answer was brought to you by the really rough estimate organization, where we estimate things that cannot be properly determined from my work computer.

I have read a lot about cob being used in England, which is probably wetter on the average than most places in the U.S.

Well, maybe whomever does it here doesn't do it right, but even the old masonry structures here need regular tuckpointing or they'll crumble. When I lived in California, some of the oldest buildings, if not the oldest buildings, were adobe and I saw some nice cob.  Not so here.  Could be a combo of high humidity, windy storms, and strong freezes... I'm not an expert.

I imagine a freeze-thaw cycle is the culprit. If ambient humidity saturated the outer layers of cob and then froze, the moisture would expand, probably causing some of the material to slough off.

I think that a proper roof overhang takes care of most moisture-related cob issues, and sealing that with a natural hydrophobic plaster might do wonders, too.

I would suggest reclaimed cinderblock before tires. Hell, I'd suggest a conventionally built building before tires.

Which is best depends on your goals. I would probably look to a rubble trench foundation and earthbag, if I wanted something bullet-proof, or a pallet structure cobbed on the inside and with that aforementioned hydrophobic natural plaster on the outside(I think it's essentially cob that's treated with olive oil at a certain stage in the cure).

In either case, I would overbuild on the structure to put a bigger hat on it than strictly necessary. I would also design and orient the structure in such a way that it harnesses the prevailing wind to promote airflow around the building, which might help keep the ambient moisture levels around the structure low.

-CK

If I were in your shoes I would go underground, or at least substantially bermed, in your climate. The year-round underground temperature is between 65 and 70 degrees F., a very livable temperature, without need for heating or cooling! Of the three options you are considering, the only one that should be employed below grade is earthbag. With this technique, the exact composition of the soil is not nearly as critical as it is with cob or plaster for strawbale, so what appears to be very little clay in your soil is not a problem. Also, it is conceivable that a very small underground home could be built for very little money with earthbags. You greatest expense will be for a good roof. There are many underground/bermed house plans shown on my website at http://dreamgreenhomes.com/styles/earthsheltered/earthbermed.htm

Amit Enventres wrote:I live in ohio.  People have tried cob here.  It's fun to watch it melt slowly over the years because of the moisture here.  Cob, like its sister Adobe are meant for dry conditions.  Even soil cement, which I experimented with,  melts here and it probably would in other wet climates.  Cob is ok for indoors here though. I thinki straw bale might be similar because it usually has a breathable cob exterior. How's your supply of pallets?

  this is so untrue....   England specifically and alot of Europe used/use this style and it still lasts!   it does take maintenance and keeping water off the walls always helps.    

For economy, durability, and comfort I do not think anything can beat adobe, in any climate. A few decades ago in Corpus Christi, where I grew up, someone tore down a considerable mansion that was made of site made bricks. I think the bricks were burned in piles as those things used to be done, which results in bricks of varying properties that get sorted for particular use. There was no water system when the house was built and the builder, being smarter that some, brought his 'water' to the hill top on the hoof. The bricks and of course the mortar, having been made with goat milk were, after 100 years extremely hard, requiring dynamite to remove. That house had been thru several Gulf coast hurricanes and as far as I know never suffered wall damage. Stabilized adobe and compressed earth blocks are also relatively water resistant. Even plain adobe can be used if the wall has a waterproof 1st course and a sufficient overhang. Do not, in the case of using regular adobe, install a sprinkler system that hits it every other day. You can also install waterproof plaster if you want that appearance. I personally would never consider a straw bale house in a climate that did not stay frozen for several months a year, in fact, having thought about it for decades, would go for the compressed earth blocks. I tried the earth bags for a small structure and my conclusion was that the labor was way too much for the results.

Adobe is a thermal mass material and provides little insulation. It evens out the temperature swings and provides great comfort, especially if it is provided with an insulating layer on the outside. I live in an old adobe house that I provided with 1 1/2 inches of foam insulation on the exterior covered with stucco. This house is very comfortable and economical to live in.

Strawbale is a great insulator and the thick walls have a nice look.

What if we combined all 3.
Earthbag for the stemwall
Strawbale for the wall
Cob for the floor, plaster, and the "glue" to join the strawbale.

I would use regular "plastic-based" closed cell insulation for the floor and roof.
The roof will also include some lumber.
What type of bond beam? wood?

You could also do a insulation core with chicken wire mesh + ferrocement stucco for the roof too vs lumber.

What you describe sounds quite doable and would result in a very comfortable and sustainable natural home in most any climate. Strawbale walls often do have wooden plates at the top to connect the roof to.

Thanks for your post, and the helpful replies.  Someone mentioned insulation.  How does it work to add insulation to the earthbags, on the inside with the soil?  I have read of people adding scoria, rice hulls, even styrofoam peanuts.  Are these helpful?  Do they detract from the strength of the bag?  What happens after several years when the rice hulls degrade?  Will the empty space they leave still serve as insulation?

Tom Connolly wrote:Thanks for your post, and the helpful replies.  Someone mentioned insulation.  How does it work to add insulation to the earthbags, on the inside with the soil?  I have read of people adding scoria, rice hulls, even styrofoam peanuts.  Are these helpful?  Do they detract from the strength of the bag?  What happens after several years when the rice hulls degrade?  Will the empty space they leave still serve as insulation?

Adding insulation with the soil is generally counter-productive; it looses most of the insulation value and may detract from the soil forming a firm block. Scoria, rice hulls or styrofoam can be used as fill in their own right, and would provide excellent insulation, although you have to be careful because only the scoria would be weight bearing. To insulate earth-filled bags it is best to add a separate layer on the outside, which could be commercial foam, papercrete, light straw/clay or even strawbales or more bags filled with insulation.

Question: I have a "conventional" home in Cary NC where it is extremely humid in the summer and snow in winter. My house has a sloped crawlspace (where water heater, dehumidifier and furnace/a/c and furnace vents , plumbing are located. It is a concrete block foundation and brick exterior on the main level, then siding on the 2nd story. Timber framing. I want to remodel my home one room at a time by removing the sheet rock and insulation and mixing just hemp hurds with clay (not lime) and water to form the walls/insulation and then put clay plaster as the finish. Is this doable? Is it ok to put the clay/hemp right up against the exterior brick and timber framing? Is there any moisture issues with doing that? Eventually I want to remove the flooring and fill the crawlspace with rock, sand and earth and top with hemp/clay ?? for a finished breathable earthen floor and relocate the water heater and hopefully remove the dehumidifier. Since I have timber framing for the structural aspect of it and I understand hemp is not structural (although the clay should be sturdier than lime) would this be ok??? Is it possible to do this from the inside out? Since it is winter now, I would like to do the interior walls and save any exterior projects for the summer. Thoughts???

Janeen Reavis wrote:Question: I have a "conventional" home in Cary NC where it is extremely humid in the summer and snow in winter. My house has a sloped crawlspace (where water heater, dehumidifier and furnace/a/c and furnace vents , plumbing are located. It is a concrete block foundation and brick exterior on the main level, then siding on the 2nd story. Timber framing. I want to remodel my home one room at a time by removing the sheet rock and insulation and mixing just hemp hurds with clay (not lime) and water to form the walls/insulation and then put clay plaster as the finish. Is this doable? Is it ok to put the clay/hemp right up against the exterior brick and timber framing? Is there any moisture issues with doing that? Eventually I want to remove the flooring and fill the crawlspace with rock, sand and earth and top with hemp/clay ?? for a finished breathable earthen floor and relocate the water heater and hopefully remove the dehumidifier. Since I have timber framing for the structural aspect of it and I understand hemp is not structural (although the clay should be sturdier than lime) would this be ok??? Is it possible to do this from the inside out? Since it is winter now, I would like to do the interior walls and save any exterior projects for the summer. Thoughts???

For your walls what you propose is probably doable, but I question whether you would ultimately benefit from doing it. Hempcrete is not any more insulating than the existing fiberglass, and you could keep the drywall in place and apply an earthen plaster over it to achieve the same effect with considerably less work and expense. If you prepare the wall with a gritty surface it will hold the earthen plaster.
The reason that lime is used with the hemp hurd is that there is a chemical reaction that happens and the result is quite stable; I am not sure if clay would work as well. Hempcrete can be used in wall cavities, though, so this approach is possible.
As for your idea of replacing the crawl space with fill and creating an earthen floor, I suppose that this is also possible, but you would likely be compromising access to the plumbing and other utilities located there. Floors do not generally need to be breathable. If you wanted the earthen floor for its thermal mass, you could also achieve this by the use of tile or brick laid on the floor... as long as the sub-floor was made sturdy enough.