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Building a Cob House

[ 18 ] March 12, 2011 |
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Tim Green Cob HouseIn a time in which we are increasingly hearing scary statistics about the fate of our planet, the way forward in the field of sustainable, green building may just be to go backward.  This is certainly the case for people demonstrating a growing interest in building earthen homes and structures using an ancient method known as cobwork or cobbing.  Cobbing, believed to have originated in the Maghreb as early as the 11th century, spread into wide usage across many parts of the rest of Europe as the main building style for homes.  The name of this style of building comes from the word cob, which is the name of the building material itself, formed of a mixture of earth (such as clay, sand, and other soil), straw, and water.  Despite what the materials may imply, this substance, when dried, is fireproof.  It is also inexpensive, and naturally cool in the summer heat and relatively easy to heat in the winter.

Many homes built of this material centuries ago still stand and remain in use.  Pictured here to the left is a cob house in England, believed to have been built in the late 1700s. (Photo by Tim Green, http://www.flickr.com/photos/atoach/4927564858/) These homes typically have thatched roofs, while small but efficient fireplaces with chimneys provide warmth when the weather is cold.

The appearance and texture of cob varies from region to region, depending on the available natural resources and their characteristics.  As such, cob is one of the most versatile building materials on earth.  It can be molded and shaped into whatever form is framed by the builder.

This photo on the right is of a cobwork home in the Pacific Northwest of the United States illustrates the potential for great architectural diversity when designing cob homes. (Photo by Gerry Thomasen, http://www.flickr.com/photos/gerrythomasen/1539506253/)What would be impossible for building with bricks and concrete blocks – specifically, achieving low cost, rounded shapes and archways and even rounded windows and doors – is entirely doable with cob.  Notice the plants sprouting from the rooftop.  Many cob house dwellers prefer earthen roofs with natural, living plant material forming a natural insulation for the structure.

A recent resurgence of interest in cob building has led to several emerging Web communities that provide support and information for each other, as well as interested newcomers.  A quick Google search will turn up several how-to guides for building with cob, and some considerations builders may have to address , including building codes in locations across the United States .  Because cob building is so easy, even people who have never built anything before can catch on after attending a short workshop series, or single, day-long event.  One of the popular, first cob projects is to build one’s own cob oven.  The oven is often the starting point, even for a house, though it is equally popular as an end-product, used as a decorative outdoor cooking area.

Cob home building among the most sustainable on the planet, not only because of the materials it is made of, but also the fact that the house will eventually return to the earth whence it came, naturally, at the end of its life (which is, conveniently, not until people utterly abandon it, since cob houses can be easily repaired, modified, and added onto over hundreds of years.)

Cob is also energy efficient, owing to walls that are often a full meter thick.  Building with cob allows more customization than other forms of building, and are capable of more truly reflecting the tastes and aesthetic inclinations of their dwellers.

To learn more about cob building, visit the resources below:
http://small-scale.net/yearofmud/
http://weblife.org/cob/
http://www.cobprojects.info/

Melonie writes about sustainable living, technology, and travel.  She writes for www.directsattv.com. This post has been syndicated by Nathan Brown, the recruiter for Dancing Rabbit Ecovillage’s environmental engineering internships and provider of solar panel building videos.

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Category: Renewable Energy, Sustainable Living

About Everett: Everett writes about voluntary simplicity. This blog catalogs his search for "the good life" as he tries to strike a balance between work and play; freedom and responsibility; simplicity and comfort. View author profile.

Comments (18)

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  1. Aim says:

    yeah cob is pretty good, but I prefer straw bale myself, good read though.

    Aim

  2. Big Al says:

    The idea that folks are trying to save the planet is really funny. I’m off the grid to make an inexpensive way of life and to cut reliance on the grid that soon might go away. For me going off the grid is about saving myself, NOT the earth it is 4.6 billion years old it will still be here long after were gone. As far as Co2 emmissions go the plants and trees are loving it and growing faster than ever. Evident in the growth rings that is why people are going for logs that have been underwater for trees that were cut 50-100 years ago for the tighter grain S l o w e r growth less Co2. I’m a sawyer I see these things.

  3. Chris says:

    I presume this is for area’s that do not get a huge amount of rain per year? I know England can be wet, but it is as wet as western Washington State? We live out in the temperate rainforest, 130″ plus a year. Any thoughts on that or directions you might point me? I have as of yet been unable to find any real information on that. Would love to give this a try but suspect it may be a frustrating up hill battle if even achievable.

  4. Big Al – I think the idea behind “saving the planet” is actually really about saving ourselves, or – at least – our children’s children. I don’t think anyone is under the impression that the earth will “die”. Instead, it will reach a point where WE will die. The earth will go right on as it always has after the extinction of a species. Well, until our sun turns supernova or something of that magnitude happens. So we’re all on the same page. And we all want to save money too. I think we need to focus on where we agree a little more and less on where we don’t. Here is an article about building cob houses, and out of all of the information or opinion you can provide, you choose something as off-topic as the motive behind it, rather than contributing your knowledge as a sawyer to help offer something constructive, like which wood is best for cordwood homes, etc…

  5. myfree spirit says:

    so what is the best cordwood to use for constuction?? also what are some pros and cons of cob vs. straw bale..any ideas?

  6. I’m not sure which cordwood would be best (locus maybe?) but I can tell you that straw bale limits you more on the shape of the structure and is more expensive. I helped build a strawbale home once and they tend to be very square, while still wavy. With cob and cordwood – especially cob – you don’t have to bring in as much material from the outside (unless you have a good on-farm source of straw with a bailer) and you can make all kinds of different shapes.

    Maybe Big Al will know what the best wood for a cordwood home is.

  7. Big Al says:

    Ok guys sorry for the raw comments. In my opinion depending on where you live the best cord wood to use for your structure would surely be what is native around you and available free or for the work of getting it. If you live in Florida cypress wood is best or long leaf yellow heart pine. If you are from the north locust is best. if you are from the west say northern california redwood. All of these woods resist rot and fungus naturally. If you have to use soft woods you can treat it with non toxic anti freeze,borax and boric acid mixture and saturate the wood with it once a year and prevent fungus and dry rot and as a bonus it will kill termites as well. To make the solution you will use one gallon of nontoxic RV antifreeze, one pound of borax (20 mule team type) and one pound of boric acid. I have found that walmart has this roach pruf stuff for killing roaches(99% pure boric acid)for 3 bucks a bottle, powder form. In a bucket mix it all together till disolved and spray on wood till it runs off I usually go over the area twice..This stuff works..Do the research for your self if you like..Big Al

  8. Awesome, thanks Big Al! We live in the Northeast. I figured Locus would probably be best because it is all over the place, grows back quickly and gets hard as stone once cured. It is what we go for when choosing firewood for the all-night burn.

    I had no idea about the use of boric acid to kill bugs and prevent fungus. If you already have termites would that be an effective treatment, or would it be too late by then?

    Cheers,

    E.

  9. knotty head says:

    how much does the average cob house cost

  10. Big Al says:

    Hey guys and gals, The boric acid and borax treatment will kill termites if they are already in the wood too. The idea behind using non toxic antifreeze is it is drawn to moisture in the wood and carries the chemical with it deep into the wood where it dries and stays. This stuff can be used around food stuffs(if you had to)or animals/People with out worry of poisoning anyone..
    Big Al

  11. Betsy says:

    As I was reading this it sounded like cob is very similar to straw bale building. What are the main differences? It seems like the straw bales might be easier to work with.

  12. Big Al says:

    Betsy, Cob is made with straw,dead dry long grasses,anything that has strands that will hold clay together for basic cob. Basically cob is a covering that you will cover over straw or earth filled bags that you build with. If you build with straw you will need to have a frame of timber then you will fill in between with bales of straw then you will stucco over with the cob. Do some searching on youtube and see some of the how to videos in the subject. Hope this helps

  13. Mary says:

    My family and I built our house out of cob in a method called cobwood, where cob is combined with the cordwood building technique. We’ve been living quite comfortably in it for three years now, in a very cold climate. Last year we also built a small barn using the same method. Pictures of that process on my blog: http://lundkids.blogspot.com/2010/11/our-little-cobwood-barn-project-is.html

    Blessings!
    Mary

  14. Cob is a fairly universal building material and has been used in many parts of the world and climates. It can make up the entire wall as they do in Ireland and England, some parts of Africa and has been used this way in the USA. Frames for windows, Doors are usually set up and “cobbed” into place. Once dried and Plastered with a lime/cob minus the straw mix it will withstand high moisture areas. If you really worry about moisture, you could “fire cure” it like a few tribes in Africa do. In this instance you would not cob in framworks for windows or doors until after the fire cure. Of couse this means you would be sweeping out all the ashes after the burn before you could continue the build. I’ve been researching cob building for the last 10 years. I prefer it over straw bale construction.

  15. Kat says:

    hey all,

    i noticed a couple posts up that big al mentioned you use cob to cover over straw bale and earth bags. now, i haven’t done a building out of either of these materials yet (though, i plan to once i find some affordable land here in the pacific nw) however, from everything i’ve read and watched i believe that’s an incorrect assertion. cob you can build with outright. it is load bearing and is the actual structure itself, not a covering. straw bale is also load bearing. there are building codes for oregon where the bales are load bearing, no timber required. it’s been a while since i read the codes and they may have changed, but if i remember correctly you can build up to ten bales high before you are required to use a timber support structure. of course you need to reinforce/straighten the walls by shoving re-bar through the bales along with a few other code requirements, however, my post is becoming a story, so lastly i’d like to point out that you use plaster to cover over said cob/straw bales/earth bags and finish with a lime wash to keep the weather out.

  16. Kat says:

    i’d like to amend the last post, i came across a video yesterday where they DID, in fact, cover their straw bales with cob, before they used their clay/plaster layer. the bales were load bearing without a timber structure, though.

  17. J-Dotson says:

    Can this method be used in the U.S.A.? I mean building codes etc. Not sure what they can do to you if do use this method of building.

  18. Frank Berry says:

    Im a 49 year old male who has been downsized, laid off, fired, jobs went overseas, etc.

    I’m searching to find a builder who needs volunteers to build existing projects…but I need to exchange my work..which will be extensive and then build my own..after that…I’ll help others to do the same.

    It’s as simple as that…I don’t have thousands of dollars of money to “go back to school” and partake in training.

    Thanks – any advice…very appreciated anywhere that COB building is being done..it seems to be the most reliable and sustainable in any weather climate.

    Good Works-

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