Education about Cob Building
ASK THE EXPERT ADVICE
Links to the Ask the Experts page

Q: I am 26, and have only recently been exposed to the concept of green building. I am extremely excited about the idea, but have no building experience and very very little money with which to explore its possibilities. Do you know of anybody or group that needs a worker, that would be willing to to teach, house, and hopefully feed me (if possible), in exchange for free labor, cooking, and childcare? I'm especially interested in places in the northwestern U.S., though anywhere would be great. I am at a loss as to where to begin, and I would appreciate any direction you can give me!

A: There are some organizations and individuals out there who offer work trade opportunities of the sort you are seeking. I don't know of a centralized listing of such opportunities. You could try doing a web search. The community where I live, Emerald Earth in Northern California, offers a work exchange program from April through October, including natural building as well as organic gardening and other projects. You can get more information at our web site: www.emeraldearth.org. Another organization nearby which offers internships is the Solar Living Institute: www.solarliving.org.

Most of the work exchange programs that I know of will offer some instruction and opportunities to learn in exchange for lots of your work which may or may not be directly related to the things you are most interested. They are not focused natural building training. It may be difficult to find a position doing natural building full time without any experience whatsoever. You would be better off if you could scrape together the funds to take at least a 1-week natural building workshop. In addition to learning some basic skills, a workshop also provides you with an instant network in the form of the instructor, workshop host, and other participants. Listings of workshops and some internships can be found at www.cobworkshops.com and www.thelaststraw.org/calendar.html.

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.