Education about Cob Building

Michael G. Smith has a background in environmental engineering, ecology, and sustainable resource management. In 1993, along with Ianto Evans and Linda Smiley, he started the Cob Cottage Company, a research and teaching group focused on reviving and improving traditional forms of earthen construction. He is the author of The Cobber's Companion: How to Build Your Own Earthen Home (Cob Cottage Co., 1998) and co-author of The Art of Natural Building: Design, Construction, Resources (New Society, 2002) and The Hand-Sculpted House: A Practical and Philosophical Guide to Building a Cob Cottage (Chelsea Green, 2002). He teaches practical workshops and provides consultation to owner-builders on a wide variety of natural building techniques, site selection, and design. He lives in an intentional community in Northern California. His informative website is www.strawclaywood.com.

Questions and Answers

Q: I am from Colombia, South America. My wife and I want to build our own cob house. Could you recommend a good and very practical book, or do you know about workshops in Colombia?

A: Although I can't claim to be impartial, I would say the best hands-on book for cob builders is "The Hand-Sculpted House" by Evans, Smith, and Smiley (Chelsea Green, 2002). I'm afraid I don't know of any workshops in Columbia. The closest that I'm aware of would be in Mexico or Argentina.

Q: I have an undergraduate degree in Geography and Environmental Studies.  I am not sure yet what my options are for a Master's Research Degree - I am trying to brainstorm at the moment for research ideas.  Once I have an idea, I will put together a proposal and then try to find the university professor who would like to supervise my research.  I am not sure what needs to be researched about Cob.  Here are two potential topics/questions for my research:

1.  Does Cob withstand freezing temperatures?  Every time I speak to people about Cob in Northern British Columbia, I get questions about Cob's ability to withstand freezing temperatures - they don't believe that it would be a solid building choice for northern climates.

2.  What is the "Thermal Envelope" of existing Cob houses?  A "thermal envelope" is everything about the house that serves to shield the living space from the outdoors. It includes the wall and roof assemblies, insulation, windows, doors, finishes, weather-stripping, and air/vapor retarders.    

Anyway, if you have time to think about any other questions about Cob that need research, even if they are scientific in nature, it would be helpful for me to get some different ideas and feedback. 

A: There is no real mystery about cob's ability to withstand freezing temperatures. There are plenty of examples of cob buildings in very cold climates (including Denmark and various parts of Canada) that show they can.

The more pertinent question is, is cob the best choice in very cold climates? From a purely thermal standpoint, I would say no. Cob is not a very good insulator, so heat will be lost through the cob walls at a rate inversely proportional to wall thickness and proportional to the square of the difference in temperatures between inside and outside the building. A better-insulating material like straw bale, if such is available, makes more sense where winter climates are cold.

What could be interesting would be to find the exact point where the tradeoff in energy efficiency points to use of straw bale over cob. Some straw bale advocates believe that straw bale buildings, because of their much higher insulation value, are more efficient in every climate. Many of us believe that at least in Mediterranean climates, where winters are mild, summer days hot, and nights cool, that cob or other high-thermal mass building systems (such as adobe, rammed earth, and masonry) are more efficient overall because of their increased cooling capacity. Some computer modeling supports this thesis.

It would be great to create a computer model into which various types of natural buildings (with factors such as insulation value, thermal mass, and wall breathability or air exchange) could be combined with various climate factors (and also ideally passive solar design features) to determine which wall system is most thermally efficient under different conditions.

I imagine this is a significant programming task and would also require some fairly sophisticated engineering analysis. There are a handful of other engineering-type questions of this magnitude or greater that would be very useful for someone to put a couple of years into researching. I'm not getting the sense that that is the sort of thing you are able to take on.

Are you up for either doing either physical engineering testing in a sophisticated laboratory setting, or complex computer modeling? Or
are you imagining that you will be compiling and analyzing existing data? In the latter case, I have to tell you that there is not a whole lot to work with. Frankly, building yet another cob structure outside of a laboratory setting and doing some simple tests on it is just not going to be very useful. we have plenty of anecdotal evidence already. What we really need at this point is more really clear, scientifically unimpeachable data that can be used in the development of codes and suggestions for builders. Besides thermal issues, other categories of research include seismic safety and design, and the development of simple engineering methods useable in the field to determine compressive and tensile strength of cob samples, and therefore to determine the best mix for a given soil and safe load-bearing capacity. For further details on the needed research regime, contact John Fordice, a California architect who is leading up the cob codes project and has developed an extensive testing regime for cob.

I suppose a less technical but still useful research study would be to compile the experiences of everyone in North America who has received official permits for cob buildings (especially houses) and to put all of that information, with whatever engineering has been done already, in a form easily accessible (on the internet I would imagine) to others applying for permits for cob. Without knowing more about your background and research capabilities, that is the best suggestion I can come up with.

Q: I am an aspiring natural builder from the United States. I have a degree in architecture from the University of Michigan (in the States), I've participated in Ecosa's hands-on natural building workshop, and I am now applying to several apprenticeship programs in natural building (focusing in cob) for the spring-summer of 2009. My wife is an international school teacher. We are currently living in Damascus, Syria and both intend to continue living and working internationally. While I haven't yet completed or even been accepted to an apprenticeship program, it is imperative that I begin looking for a potential job as soon as possible so that she knows where to apply for the 2009-2010 school year. Would you be able to give any suggestions for finding natural building work internationally? To clarify, by work I do mean a paid position. While I would be willing to volunteer a portion of my time, I have school loans breathing down my neck. However, International schools generally provide housing and currently we are getting by while I tutor part-time so the pay does not have to be great by any means.

A: As far as finding paid work goes, I can say that there is work out there but that there is no formalized system for finding it. Most positions are filled word of mouth by people known to the contractor or home owner. This sort of networking tends to happen either by developing connections in a local community or by making relationships with other natural builders. However, I would encourage you to put the word out that you are available and looking for work. Some possible vehicles include the Last Straw Journal, and The Natural Building Network website. Once you have completed an apprenticeship program, you will have a lot more to offer to potential employers. However, it is still very common for people to expect to volunteer for a season or two to build up their skill set before finding paid work as a natural builder.

Q: Do you know about the Mud Girls? They do an innovative labour for learning program that includes moms with children. www.mudgirls.ca I haven't found many other workshops that allow children (Firespeak has done it in the past) but am looking; if you know of anything please do let me know. I want to learn but need to do it as a family activity.

A: I'm surprised to hear you say this. I've been teaching natural building for 18 years and have never been part of a workshop that didn't allow children. Although it may not be specifically mentioned in the workshop description, most natural building instructors that I know are happy to have children participate, as long as their caregivers make sure they are not disruptive during lectures and other focused times. Certainly this is the case with Cob Cottage Company and with my own workshops. Good luck!

Q: I am currently based in Ahmedabad, Gujarat and work with a group of slum children. We are in the process of "building" a shelter to serve as our school space and feel that making a simple cob structure would be a wonderful hands-on lesson for the children. Do you think this is a feasible project? The children range from 12-16, but are quick learners and very resourceful. Also, if I come up with a basic design with the kids, would you be able to guide me on the practicality of it? And perhaps most importantly, how do I make it rain proof?

A: How exciting! What a great idea to involve the children in building their own learning environment. Yes, I believe it is feasible, although it will take a great deal of work and commitment. Children of that age should be physically able to do every part of the process of building with cob.

If you want to take on this project, I would strongly recommend getting your hands on some books that can guide you through the process. Good ones to start with are "The Hand-Sculpted House" by Evans, Smith, and Smiley, as well as "Building Green" by Snell and Callahan. There are so many technical details to consider that it's probably not practical for someone to guide you entirely over the internet. But if you read those books and have further questions, I'd be happy to answer them then.

As far as rain proofing your building, the solution is a roof that doesn't leak. Ideally, the roof overhangs will be wide enough to keep rain completely off of the walls, but if a bit of rain is blown onto the walls occasionally, it shouldn't be a problem.

Q: I have sensitivities with chemicals so have to use any and all materials that do not off-gas, or recycled materials that are at least five years old. Even some natural (woods) can off- gas & produce chemicals (formaldehyde). I have yet to hear any discussion in the alternative building movement of the 'need' of people with sensitivities and there are a large number of us who face many challenges on a daily basis and need a space that does not cause us to get sick. People like me have the least impact on the environment; we tend not to be big consumers, but most of us are too sick to be vocal...but I hope to change this over time by building a structure on my land as a respite for those who would like to go there and use it & bring attention to this issue in the building process.

A: I've had a number of chemically sensitive people take workshops from me, so I'm aware of the unique potential that natural building has to provide healthy housing for sensitive people. Part of the irony is that although natural materials such as cob are very inexpensive, they require a great deal of labor to turn into a home, which can be challenging for people who are ill. I wish you the best with both your need for a supportive home for yourself in which to get well and your desire to bring greater public attention to this issue.

Q: I would like to learn how to build an earth house.

A: If you'd like to build a cob home, this is what I'd recommend. First, read "The Hand-Sculpted House" by Evans, Smith, and Smiley. Second, I'd recommend taking a hands-on workshop. If you know you want to do cob, the Cob Cottage Company in Oregon is a great place to learn. There are also teachers in Canada, although mainly in southern BC. I also teach hands-on workshops, usually covering a wide range of different natural wall systems and finishes.

Q: My husband and I are going to buy some property in Christmas Valley, Oregon, and we are wanting to build a cob home for our family. Our goal is to start building 2-3 yrs from now. We are currently living in Newport Oregon and had heard about a cob home class here in Oregon. Do you know how we could get into one of them? We want a hands on experience before we build our own.

A: There are several organizations that teach cob workshops in Oregon. Start with The Cob Cottage Company (www.cobcottage.com). If you can't find what you want there, then look at cobworkshops.org.

Q: We are thinking about moving from Norway to Sierra Leone - West Africa, where my wife's from. I have taken interest in building with earth, and the plan is to build with earth in Sierra Leone. I have been looking for information about the traditional method used there, but I haven't found very much. I'm thinking about the method where a framework is made of wood (poles), and the framework is then filled with earth. I was looking for information about the strength for this kind of structure, and if it's possible to build two stories. And also strength compared to an earthbag-structure.

A: I imagine that the construction technique you're referring to in Sierra Leone is some variant of wattle and daub. Wattle and daub has historically been the most popular building system in the world. It has certainly been used to build 2-story buildings and more. The strength of the system depends on the strength of the wooden framework that does all the major structural work. A 2-story earthen structure would require quite heavy wooden beams and posts to be safe. Alternatively, you could make the structural framework our of steel or concrete and then fill in with a combination of sticks and mud. If earthquakes are a concern, you will need to find a way to introduce shear resistance into the structure, especially with a multi-story building. This could be done using wooden cross-bracing, or steel strapping, or concrete shear walls, for example. If you can't find good functioning examples of the sort of building you want, it might be wise to get an engineer involved.

Earthbag is a very different system. It's essentially a form of masonry using bags of earth as the masonry units. There is no need for a structural framework of wood etc. because the bags are very strong in compression and they bear the weight of the roof or of each other, and shear strength is maintained by strapping the layers of bags to each other. The design is limited in some ways - you can't have excessively large openings, for example. Again, if you plan to build a large structure it might be wise to get professional help with the design.

I would strongly recommend attending some trainings on earthen building techniques to get hands-on experience with the sorts of techniques and materials you intend to use. Hopefully you can also find skilled builders in Sierra Leone who will be able to help make your dream come true.

Q: We currently live in GA but will be moving just across the state line to AL at the beginning of summer. We are considering building a cob house throughout the spring for us to live in, but we have no experience and know no one who does. We are a family of 4 who has fallen on hard times and has had our rental home sold out from under us twice now. We are just wanting a place that is ours that isn’t going to kill us financially that we can build while we are still in the process of moving.

A: Building a house is a major undertaking, and it pays to be as well-prepared as you can be. I would strongly recommend reading “The Hand-Sculpted House,” which has a great deal of useful information not only the technical aspects of building a cob home, from foundations to finishes, but also on essential pre-construction considerations such as design and site work. After reading the book, it would serve you well to get some hands-on building experience before starting on your home. You could either take a workshop (see cob cottage.com and cobworkshops.org for listings) or find someone who is building in your area that you can work with for a while. You do not want your very first building experience to be on your own home if you can possibly avoid it.

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