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cob vs earthbag vs straw bale for southern appilachian area  RSS feed

 
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anyone have experience with any of these in southeast us. looking for ideas. I'm leaning toward starting a cob building but earth bag and straw bale are also attractive. these seems to be high clay content in soil on the property but there is also lots of what some people call chert which is a more sandy soil with lots of small chips of rock.
one thing that concerns me is there are subteranian termites everywhere. in one summer they built free standing tunnels up through 4 feet of cedar shelving to get to a cardboard box in the root cellar and eat normal pallets in 1 to 2 years many other places on property. although i've found the termites don't mess with anything made of red cedar. maybe using red cedar shavings in the cob mix. This is why I'm asking. I don't know and want to be sure of what i'm doing before investing time energy and money in project.
 
pollinator
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Location: northern California
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If I were just starting out I would arrange a visit to Earthaven Ecovillage.  There are many examples there of these construction techniques and you may be able to find out by observation and conversation what works and what doesn't.  Even from my several visits there I know that mold and mildew are important issues with these methods and very careful attention to their prevention needs to be planned from the outset.
 
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It is not clear from your post as to the relative proportions of clay vs. sandy, chert soils.  Considering your area, if you have termite issues, you may also have fire ant issues.  Since cob is generally mixed and packed in a monolithic construction mode, it may be safer than either earth bag or straw bale.  Most earth bag construction does not call for much compaction.  Either termites or fire ants may be able to penetrate into the non-compacted soil interior and take up residence, not a pleasant possibility.  Straw bale construction usually uses a form of cob, but due to the thickness, the cob coating may be thin enough for burrowing insects or rodents to breach.  Your observations on red cedar are useful.  Red cedar tends to deter insects of all types, therefore, using red cedar in cob might also deflect fire ants or other insect pests.  Just ensure sufficient straw in the cob to provide the longitudinal support to the mix.  Observe the cob carefully when placing to keep unmixed straw or other materials from forming potential voids.  

As a thought, have you considered rammed earth construction?  Similar to cob, it allows a monolithic wall that resists intrusion.  If you have both clayey and sandy soils, it should be easier to get a good ramming mix.  The advantage to this is the more vertical and even walls that can be constructed.  Constructing walls of rammed earth blocks also would allow mismatching from one vertical run to the next, making intrusion more difficult.  Rammed earth can also be placed in old tires to allow tighter vertical walls.  bolt tires together and ram the earth into the tires.  Walls of this type of construction are incredibly strong and I have seen concrete trucks driven on such a rammed earth wall.  Just ensure that there is some method of providing a solid vertical connection from the foundation to the roof to provide resistance to high wind forces.  If you are in some areas of the southeast, such as the Piedmont of South Carolina, ensure there is reinforcement to any type of construction used to cover earthquake loading.  Check the USGS earthquake maps (https://earthquake.usgs.gov/hazards/interactive/ ) to see what risk area you live in.  Fortunately, resistance to earthquake is also good for wind pressures so long as care is maintained to keep a strong vertical connection (known in building codes as a continuous load path, for the roof.

Hope this is not too technical.
 
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Location: MA
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Richard, for rammed earth do you recommend stabilizing it with cement and just tamping it down in the form with a steel-weighted hand tool?  The videos I've seen look like the ramming pressure is on the order of 10 psi.  On the other hand the compressed earth block I've seen seems to be compressed to more like 100-1000 psi.  Before seeing the rammed earth just now, I had been wondering about using a hydraulic log splitter to make CEB, since it could deliver these higher pressures, at least on a standard brick size.  But after seeing the rammed earth, now it seems like it might be easier and faster to make larger forms with a bit of cement, since only a low tamping pressure is needed, evidently.  
 
Richard Henry
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Mike:

OK, rammed earth can be many things.  First and foremost, ensure you have the correct consistency.  if the mix is too dry or too wet, it will not compact and will come back to haunt you.  Too wet can be cured by patience and letting the mix dry in place in the forms, too dry, only tear down and replace.  Thumbnail basics,  If you are creating rammed earth, and attempting to do so by hand, I suggest finding a hyper teen who wants to join the WWE.  Tell him that he will get upper body and arms to match with the best of them.  Quick check on proper moisture - make a ball in your hand, hard as you can make it and then drop from the waist.  If it remains essentially a ball when it hits, you have the right mix.  If it shatters or splats, too dry/wet.  Beat the mix with your compacting tool (can be a 2x4 or a rolling compactor you choose the level of technology to use).  When the dirt starts to sweat, you should be there.  That is a sheen on what started as moist dirt.  The sheen means you are compacting the moisture out of the pores/voids/empty spaces between the dirt particles.  I have designed large forms to run a small puller over drawing a roller, preferably with little pieces of iron welded on to make a sheepsfoot roller.  Of course, if you have sheep, try running them back and forth.  Make sure the lifts (layers of moist dirt) are thin enough.  I have tested and failed large hydraulic compactor attempts on too thick a lift.  Really frustrating for the contractor, but what they get for impatience.  Tamping into tires is generally hand work with smaller tools and can create a fast wall where the form is left in place.  Just bolt the tires where ever they meet another tire and that wall will hold up to most natural and a few unnatural forces.  It is a great way to clean the environment and makes for faster wall construction as the soil can be wetter and that will make compaction easier.  Just try to keep water from flowing out of the work area because that will erode some of your work lower down.
 
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How about light straw-clay?  I think it's faster than cob and the house could be rectangular.
 
Posts: 33
Location: Brevard, NC
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Any of those methods of building can be used in the Southern Appalachians.  More information is needed to make a decision about what makes the most sense.  What sort of site are you building on?  How much sun are you getting?  What is the purpose of the building--are you living in it?  Does it need to stay warm?  Do you have helpers or are you alone?  How much time do you have?  How much money do you have for this project?  What is your building experience?  All of those are really factors in deciding this.  I don't think the major thermal mass methods (cob and earthbags) make sense in the Southern Appalachians unless you have an ideal spot with tons of sun.  Even then, there are lots of overcast days in which the thermal mass is not going to help you.  Strawbale provides tons of insulation but requires more building skill and can be more expensive depending on how you are doing it.  I agree with Lee Du that light clay straw is a great option--that's my personal preference for the Southern Appalachians.  On the other hand, straw bale construction is easier to get code approval for at least here in North Carolina.  

Another big issue with straw bale construction is the absolute requirement to keep all water out.  Water getting into a straw bale wall can totally destroy the wall and even cause a fire.  You have to use very good construction methods especially flashing around windows and doors.  We get tons of rain here so it is a major issue.  It can certainly be done and is done but you have to know what you are doing or hire someone who does.

Also consider that the Southern Appalachians are rich in forests.  So a locally-sourced wooden house with blown-in cellulose insulation is another good option if sustainability/low environmental impact is the main goal.

You have to have good termite barriers no matter the construction method (except cob and earthbags, I guess).  You also have to keep moisture out of the home so termites and other critters don't have a water source.

Definitely check out Earthhaven Ecovillage.  
 
Glenn Ingram
Posts: 33
Location: Brevard, NC
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Another big question:  are you pulling a permit?  Most alternative methods require an engineer or architect signing off on the structure if you want to pass code (lots of $$).  NC has straw bale in the code book now so that is easier.  The wood house with blown-in cellulose option also would comply with code.
 
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Soil Testing: Genius or Snapshot of the ever-changing?
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