Where does Cob Work?
ASK THE EXPERT ADVICE
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Q: We live in the panhandle of Florida. Would building with cob be a good idea here?

A: I don't know much about the geology or climate of that part of the world. And I don't know of any cob houses in that vicinity, although I do know an experienced cobber who is currently living in Tallahassee. If there is clay, there is no reason why you can't build with cob there. Cob has been built successfully in very wet places like British Columbia and Wales. If you get very frequent rain you may want to put up a big tarp over the site during construction, or build the roof first. As long as it is carefully designed and built (good high foundation, adequate roof overhangs, protective plaster if necessary) it should last a very long time. However, that doesn't necessarily mean that cob is the most suitable building material for that area. High mass materials like cob can be great at passive cooling, but only if there is some way to cool them down. In a dry climate like the high desert, even when daytime temperatures are very hot it still gets cold at night and the heat absorbed by the cob during the day can be discharged. In a hot moist climate where nights are warm, high mass materials lose their passive cooling abilities. You may need to augment with mechanical cooling. And a lower mass building system (like straw bale or wattle-and-daub for example) might be more efficient. But I don't know the climate of the panhandle well enough to say for sure.

Q: I am interested in building a natural home in central Vermont. I am very interested in cob but am confused as to whether it is a good choice for the climate of central Vermont. What do you suggest?

A: Like other earthen wall systems, cob does not have a very high insulation value per thickness (less than R=0.5 per inch.). One way
to get a higher R-value is to build a very thick wall. The traditional 3-foot-thick cob walls in Devon may have the equivalent of R=15 or so. The problem is that in a very cold climate such as yours, all that mass will be constantly losing heat to the outside, especially on the north side of the building and other parts that never receive direct sun in the winter. (If the wall gets regular sun on the outside, solar warming will make up for some of the heat loss.) Generally I would not recommend using cob for exterior walls where winter temperatures stay below freezing during the day. However, there can still be a place for cob in every climate. As interior walls, surrounded by a highly insulating envelope (such as straw bale), a massive material like cob helps to maintain a consistent interior temperature, preventing both overheating and overcooling. An especially efficient place to put your thermal mass is close to your heat source, so build a sculptural cob hearth and mass wall around your wood stove. That's my suggestion for very cold winter areas: cob for interior walls (and possibly south-facing exterior walls if you get very regular sun through the winter). The only exceptions would be for buildings that don't need to be heated or if you are building a very tiny building, in which case the amount of heat lost through the walls may be negligible anyway.

Q: My husband and I want to know if there are any earth homes built in any areas in Oregon, and are there building permits for these earth homes in Oregon?

A: There are many earthen buildings in Oregon, which is the center of the North American cob revival. Many of them have been built without permits. Some have agricultural permits. I'm not sure whether there has been a permitted cob house in Oregon yet. Contact the Cob Cottage Company at 541-942-2005 or www.cobcottage.com. They keep fairly close track of what cob homes have been built around the state.

Q: I am an architecture student doing a building project right now. My site is next to a lake, and Ii want to know whether it would be safe to build with cob there?

A: It is not wise to build a cob structure in a flood plain, where the water level is likely to rise high enough that the building will be inundated. Of course, you probably wouldn't want to build anything else there either. Other than that, I can't think of any problems with building cob structures near a lake.

C: Thanks for writing your informative and inspirational book. I am happy to report cob works in cold climates. We live in north-central Vermont in a 388 round foot cob home we designed and built. Our home has been very warm all winter with using very little fuel(wood).We have tested it by going 48hours with no fuel only sun with -20F temps outside. The key is a passive solar design and a highly efficient finnish st lye masonry heater. Keep up the good work. Live it up.

Q: I am currently a student at parsons art school of design in new york city. I have been working for over a semester long everyday researching the tsunami. As a product design student I was assigned the subject shelter for the tsunami in Thailand for our final. I have studied the area, climate, and existing shelter, but the problem that I found when trying to design shelter is that there is a deficiency of the same existing industrial products that could be transformed into housing, lack of natural materials such as bamboo, and costly mass production. Currently they being forced to live in cloned tin huts that have an oven effect in there hot humid climate. These people will be economically challenged for years to come so I want to provided them with a book that states where natural resources can be found in that specific area and different style homes that can be made out of them. I know that there is plenty of sand in thailand, and I have heard from a women who does work there that there is an efficient amount of clay and limestone, but I am stuck because the houses in thailand are raised for monsoon season. I thought it would be the perfect idea if the people could make and design their own homes out of free materials found in the earth but now I am coming across problems on how would one raise a cob home? If you would be so kind to email any information it would be greatly appreciated.

A: Although there is no tradition of earthen building in Thailand, cob and adobe have recently been introduced to the country and have been extremely well received. Last year, a group of Thai and international volunteers built a village of more than 20 earthen homes in a few months for a community which had been displaced by a large dam project. The best source of information for you would be the people and organizations that are already promoting earthen building in Thailand, including kleiwerks (www.kleiwerks.com) and sulak-sivaraksa (www.sulak-sivaraksa.org). Good luck with your project!

Q: I'm very interested in finding out more information on where (states) it is legal to build cob homes? And a contractor(s) that build them.

A: No state or jurisdiction in the United States yet has a code for cob, so far as I know. However, that does not mean that cob homes can not be permitted. Indeed, they already have been in several states, including California and Colorado. The Uniform Building Code, which has been adopted by most jurisdictions West of the Mississippi, expressly allows for "alternative materials and techniques" if they can be demonstrated to the satisfaction of local officials that they meet safety and energy standards. What this means is that in most places, to get a permit for a cob home will require a fair amount of effort to educate your local officials. There are some licensed contractors out there with experience in cob building, but most cob homes have been owner-contracted. I'm not aware of any directory of cob contractors, though that certainly would be a helpful thing to have.

Q: I live in Queensland, Australia which has a tropical climate. We have a rainy season from about Dec till April. We have a bit of humidity but I live in a a village called Kuranda which is 350 Meters above sea level. I am in love with the whole concept of cob building and have purchased your book "The Hand Sculpted House". I am being discouraged by my father to build with cob as he does not believe it would be suitable for our climate. Is there any way I could follow my dream? I of course want my home to be very strong and durable against any possible problems.

A: I don't see any reason why you can't have your dream house. Cob is demonstrably suitable to wet climates, as is shown by the thousands of cob homes on the coast of Britain, some of which are up to 800 years old. We've been building with cob on the pacific Coasts of Oregon, Washington, BC, and California for up to 20 years with no apparent problems. The 3 essentials are a roof with ample overhang, a good, high foundation to protect the base of the wall; and if necessary (where there is a lot of wind-driven rain) a lime plaster.

In a hot humid climate where the air temperature stays high all night, you won't get as much cooling advantage from cob's thermal mass as you will in a hot dry climate where night time temperatures drop. In that case I'd recommend large roof overhangs (covered porches are great for keeping the sun off your walls), lots of insulation in the roof, and plenty of opening windows for ventilation.

Q: I am looking to build a couple of small cob buildings here in the south east, one in Pensacola FL and one in Lumberton MS. FL has just overhauled its building codes to increase hurricane safety. There is a local cob builder down here who says it is impossible to have any cob building approved. I have seen how well these buildings hold up to hurricanes. Do you know of any cob buildings built here in the deep south that were accepted by a code official? Or do you know of any green-building friendly codes that I could use as an example to illustrate my case when the time comes.

A: The only cob builders I know in Florida are Christina and Craig of barefootbuilder.com. They would know a lot more about the local regulatory conditions than I do. However, I would never accept "impossible" as an answer. It may be a very political process to get a cob building approved, and it may take some time to get through the process, but I imagine if you are persistent and patient enough, it could be done. Establishing good relationships within the local building authorities is usually a good first step.

Q: A friend of mine is interested in building a cob house in the Bahamas. Unfortunately clay isn't naturally available. Could you suggest a supplier?

A: I'm afraid I have no idea what the best way to get clay to the Bahamas would be. Most likely you would have to ship it there in a container. Although ocean shipping is one of the most efficient means of fossil-fuel-powered transportation, importing large quantities of
building materials from off-island seems contradictory to the philosophy of natural building. One of the best ways to reduce the environmental impact of one's buildings is to use local unprocessed natural materials. I would suggest starting with an inventory of what materials are locally available, and then consider how to build with what you have. One technique that comes to mind is earthbags or "superadobe", a technique in which bags are filled with earth or other available materials and stacked to make walls, arches, domes and so forth. I believe at least one earthbag home has been built in the Bahamas, using coral sand as a filler material.

Q: What type of house material would you recommend for the desert environment in Arizona?

A: In a high, dry climate like many parts of Arizona, where nights can be cool but days are typically sunny throughout most of the year, you have a huge range of natural materials that can be used successfully. Traditional adobe structures work well there, as do other kinds of earthen building (cob, rammed earth, etc.). Strawbale buildings are also very successful. The best passive solar structures combine good insulation with good thermal mass; so if it were up to me I would probably use a combination of straw and earth. One way to do this would be to use straw bales for exterior walls and earth for floors, interior partitions, and thick plasters. Another would be to use straw bale on the north and west walls where insulation is most important, cob or adobe on the south and east where you get the most benefit from thermal mass.