Where does Cob Work?
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.
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.
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?
C: I am happy to report cob can work 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 style masonry heater.
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.
Q: We (my partner and I) are seriously interested and looking into building a cob home in MN (Minneapolis area). Would cob be a good material to build with in our climate and if not what would you recommend? We are wanting to secure a self sustainable lifestyle.
A: In places with cold winters, the most efficient homes are well-insulated to keep heat inside. Cob has excellent thermal mass for heat storage, but poor insulation. So an all-cob building will slowly leak heat through the walls in cold weather. You can still use cob for your interior walls, sculptural elements, hearth, built-in furniture etc., but I would recommend a more insulating wall-system such as straw bale for most of your exterior walls. The Cob Cottage Company in Oregon is promoting a system called bale-cob, which involves a relatively thin structural cob wall surrounded on the outside by straw bales. A similar effect can be achieved by using a thick earthen plaster on the inside of straw bale walls.
Q: I live in the upstate of South Carolina, and I'd love to build a cob house. I've read a LOT from cob experts lately, and when they mention codes they assure the readers of the (relative) ease of the building codes in the western states, but I've heard little of how to go about it in an eastern state. Where do I start in finding out if I can build a cob house here? I don't want to purchase land if I can't build there, and I don't want to risk not having a permit. Since I don't have the land, I would feel strange going to professionals asking them about codes without a proposed building site.
A: There's a lot of variation in the openness to natural or alternative building methods between different building jurisdictions, and even amongst different officials working for the same department. I would recommend one of two approaches. Ideally, find builders or owner-builders in the part of the world you are interested in living who have done something similar to you, and ask them about their experiences with local officials. If you can't find someone who's built with cob, look for someone who's built with straw bale, or adobe, or rammed earth. Another approach is to contact the building department directly in the different areas you are considering building, ask them if they know about cob or would be willing to learn about it, and see what sort of response you get. A conversation with someone within the building department who is interested in what you're planning to do could be a very helpful step in learning about what you will need to do to get a permit.
Q: I would love the challenge of building my own home, and cob would suit me. Do you know whether a cob house would be viable in the s.w. region of Turkey? I have land just away from the coast. In the winters it can be very wet; when it rains it is torrential, and will drop very rarely below 10 degrees and in the height of summer though it is often well over 40 degrees. What is your opinion as to whether this should be a method I should consider, as this could be perhaps the only way I could get my own home. Also it is near a fault line should this be something that I should take into consideration during construction?
A: Cob is very similar to adobe as far as its thermal and weather-resistant properties. If this is a region of Turkey where adobe (mud brick) or other earthen homes were traditional, cob would almost certainly work well there. In general, earth is unaffected by high or low temperatures. It is relatively easy to protect earthen walls from heavy rains by the use of a high foundation and wide roof eaves.
Q: What do you think of a cob house in Hawaii? My dream is to build a few of cob houses and tree houses to form a retreat center for a spiritual, creative, educational retreat where tourists are also welcome to visit so more people will be introduced to it. How can I plan ahead to meet permit standards? Do you know of any community like this that's open to tourists?
I've heard mixed reports about cob building in Hawaii. The issue is that the soils on some of the islands are too young for clay to have formed there. Kaua'i is a definite exception, and I have heard of some success on the Big Island as well. Where are you located? There are a couple of natural builders in the islands that I could refer you to. I don't know whether they have tried or succeeded to get permits for cob structures on the islands.
Q: Is it possible to build cob or adobe homes in Arkansas? The humidity is extremely high here, and I wonder if it will be possible.
A: Once built, cob homes do very well in high-humidity situations. Take for example the thousands of centuries-old cob buildings surviving in good repair on the British coast. The old saying is, "give a cob house a good pair of boots (foundation) and a good hat (roof), and she'll last forever." Foundation, drainage, and roof overhangs are all important to keep too much water from getting into the walls from below or above. Lime plasters, porches, and extended eaves will protect the walls from wind-driven rain and snow melt.
The biggest challenge of building with cob in a humid climate is the drying time. Cob walls are built with a moist, sculptable earth mixture, which must dry out to some extent as construction progresses to be able to bear the weight of the new cob being added on top. If you have very high air humidity during construction, it will slow down drying and extend the time necessary to build the walls. I don't know how much of a constraint that will be in your situation. I'd recommend building a landscape wall or some smaller project before starting in on your house. Another solution could be to switch to adobe block; that way all the drying can happen up front before you stack the blocks to build your walls. However, in that case you will need to find enough dry weather and/or covered space to make and dry all of your adobes.
Q: Hubby and I are in the full on throws of finding land and planning our cob home. We live in New Zealand and I have noticed you saying cob is not great as an exterior wall in cold climates. What is cold? haha! On the east coast of the south island of New Zealand we get little snow (sometimes 2 or 3 years go by without snow and any that eventuates never settles for more than a day) and very dry hot summers. The winter we get rain and frosts but often the sun is still out. Maybe the coldest temp is -1degrees Celsius and in the summer it ranges to 22 Celsius degrees- 32 degrees Celsius. Also, should our interior cob walls have drainage trenches? We were going to dig the foundations all as one, including any interior walls.
A: I would not consider New Zealand to be a "cold" climate. Cob should be fine as long as the exterior walls are fairly thick (say, 16-24 inches) Your plan sounds fine in general concept. As far as drainage for interior walls, the main thing is to keep ground moisture from every working its way up into the cob. If you have really good, deep drainage trenches around the exterior of the building, you shouldn't need to drain the interior walls as well. But it couldn't hurt.
Q: I live in the Mojave Desert of southern California and am wondering if there is even a possibility of cob building. All the "earth" around here appears to be sand. Do you know if there is likely to be some clay, enough to make cob? Or should I think about other techniques?
A: I'm not very familiar with your area, but I am certain that there is clay soil in some parts of the Mojave. I know about cob projects in the Joshua Tree area, for example, and I'm fairly sure there are historical adobe buildings in other parts of the region. You may have to search a little to find good soil. Chapter 8 of "The Hand-Sculpted House" talks you through various ways to search for clay if it is not immediately easy to find.
Q: I live in Mauritius Island in the Indian Ocean, tropical climate. My worry is that we do have tropical cyclones with winds up to 120-200km/hr with heavy rain falls. Would a cob house resist to those tropical cyclones? (By the way, we fortunately haven't had these strong tropical cyclone since 10yrs. But they are present in the Indian Ocean every year from november to april. What if that would happen on the Island?
A: I would be worried, too if I had heavy rains blowing against my house at 200 km/hour! My guess is that a carefully applied lime plaster would hold up to that sort of abuse, but might need to be maintained more frequently than in a less windy climate. My biggest concern would be the roof blowing off. It would seem like a heavy roof with short eaves would be ideal, which is unfortunate since longer eaves would better protect the walls from the rain. Porches are also excellent for keeping the weather off of earthen walls, but again I would worry that the whole porch would blow away in those conditions. I would want to study local vernacular buildings for inspiration. Is there a history of earthen construction in the Indian Ocean? How were roofs traditionally built to keep the rain out of the houses?
Q: I plan to move back to the big island of Hawaii in several years and would like to build with earth there, however I am concerned that the islands may not be old enough to provide the necessary clay and I am concerned about the heavy rainfall. I would like most to use cob, but am concerned about not having clay, is there a way around this?
A: I have also heard that the Big Island is too young to have clay. However, I have a friend who lives there, an experienced cobber, who swears he has made decent cob. Is the adhesive really clay, or is it volcanic ash? It may not matter as long as the resulting mixture is hard and weather-resistant enough. All I can say is, when you get back to the Island, get in the habit of testing the soils everywhere you go for adhesiveness. If you really want to build with cob, soil type may be a significant factor in selecting your location. Once you have settled on a site, you will have to make an assessment of whether cob seems like the best choice. As for rainfall, that can be an issue. You will most likely want to erect your roof first, then cob the walls in under them. If the air humidity is to high for too long, the cob will not dry and can start to sprout mold. As I recall, this may be a concern on one side of the island but not the other.
Q: My husband and I are looking to build a home in few years and have been researching various building methods. I have to say I have absolutely fallen in love with cob and straw bale construction, but I'm very concerned that the high humidity in Mississippi will cause problems. Also, whenever I mention this type of construction to my family, they want to know how it'll stand up to hurricane force winds and possibly tornadoes that often hit our area.
A: The winds, hurricanes, and tornadoes should be much less of a problem for a house made out of heavy materials like earth and straw compared to lightweight framed houses that are the norm in the US. As long as your roof is securely fastened to the foundation and walls, then you need not fear a Wizard-of-Oz like scenario. High humidity can be a problem for natural walls, especially straw bale. Atmospheric humidity per se isn't a problem once the building is finished. The more challenging part would be finding a long enough period of dry weather to complete critical stages of construction. You would probably want to build a post-and-beam structural framework and erect the roof before you begin the walls. If you go with straw bales, you can stockpile them under the roof for protection until the walls go up. In the case of cob, drying time may be slow which could draw out the construction process a little longer than it would be in a dryer climate. Wide roof eaves and porches are recommended to keep the wind-blown rain off of the walls. You may want to use water-resistant lime plasters on any exterior walls that are exposed to wind and storms.
Q: I live in Germany and am very much longing to build my own cob house here, however, I can hardly find any information about the possibilities of building a cob house here in Germany. Perhaps there must be laws preventing it, but I don't exactly understand for what kind of reasons. It cannot possibly be for the climate, as it we have approximately the same climate as in Great Britain where cob building is more and more liked and expanding. I presume it would be possible to build a cob house in a rather "straight" shape too, isn't it? For certain laws as I know in Germany, are requiring certain shapes of buildings here, but this would not be a hindrance to build cob houses either, although most builders as far as I have seen up to now, prefer round or even "fancy" forms. I do know that straw buildings are becoming more an more popular here, but at quite high costs, nearly similar to normal buildings. As far as cob buildings go, I assume that if supported by friends and family, the cost can stay quite low in comparison to traditional building. This low cost way of building seems to have no lobby here at all. But why?
A: I don't know much about the regulatory climate in Germany regarding earthen building. I do know that some kinds of natural building are accepted there, such as light straw clay. It would not surprise me to learn that there are no building regulations for cob. As you point out, there is no industry or lobby that stands to make a lot of money off of cob. As a result of that, it is very difficult to find funding for the engineering testing and code development process. One excellent source of information about earthen building in Germany is Gernot Minke at the University of Kassel, who has done a lot of research and development of various earthen building systems.
Certainly there is no reason you couldn't build a rectangular house with straight walls out of cob. I have seen many examples of this. One issue you will probably run into is the fact that cob is a relatively poor insulator compared to straw, straw-clay, or modern insulation materials. I would bet that the German building regulations are probably strict about thermal efficiency in new construction, and you may have trouble getting approval for a cob house for that reason alone. That shouldn't stop you from using cob for interior walls, built-in furniture, and so on.
As far as cost goes, as you point out, the materials needed to build cob walls are very inexpensive. However, a great deal of labor is required. If you were to hire a professional crew to build your cob home it could easily cost as much as a conventional house. The way to build a house inexpensively is to build it yourself or with volunteer labor. This rule applies to any sort of construction, not just cob. Other ways to keep costs down are to keep the building small and to use salvaged or free materials for as many components as possible. Remember that in any house the walls are usually a small fraction of the cost of the total construction. The sitework and foundation, roof, ceiling and insulation, electrical and plumbing, windows and doors, cabinets and fixtures, and floors and finishes all typically cost as much or more than the walls. So just building your walls out of an inexpensive material doesn't necessarily get you an inexpensive house unless you make similar economic choices at every stage of construction.
Q: I'm very new to natural building, but it has completely changed my mind as to what living comfortably means. I am interested in building a cob home in Troy, Alabama on a piece of land given to me by my father. Are there any limitations or restrictions to building a home like this, in this area of the country. The land is rural, and has red clay dirt and sand on it. It seems perfect for building with cob.
A: I'm not terribly familiar with the climate where you are, but I imagine it would be a good place for a cob home. Thermal mass is far less effective as a cooling strategy in climates where the days are hot and the nights are warm as well, so you may want to use some better-insulating wall systems such as straw bale for some of your exterior walls. Definitely porches and deep roof overhangs for shade. You may or may not be required to get a building permit for a house in your area. If you are so required, it can be a challenge (not impossible) to get a permit for a cob home because there are no building codes yet for cob.
Q: We are interested in finding out which counties in California support and hopefully have permitted cob homes. We are in the process of finding an area/community in California that supports sustainable building along with permaculture. Any information or guidance would be great welcome.
A: Several counties in Northern California offer special permits for owner-builders, which have lax structural requirements. This is the easiest way to get a permit for load-bearing cob in California. The counties that I know of with this provision are Humboldt, Mendocino, and I believe Lake and Nevada. There may be others. Anywhere else, you could theoretically get a permit using the Alternative Materials and Methods provision of the code, which allows you to build in a way not described by code providing you can demonstrate that safety and other requirements are met, to your building officials' satisfaction. In practice this typically involves the stamp of a state-licensed structural engineer. There are a few engineers in Northern California who are interested in cob and will provide calculations and stamp cob projects that they feel comfortable with, but of course this is an added expense. Some jurisdictions (county or city) are much more open to this sort of thing than others. I can't provide anything like an exhaustive list, partly because there have not yet been attempts to get permits for cob buildings in most places. The individual building official you are dealing within the department can also make a big difference on how your proposal is received. A friend of mine in Tuolumne County, who got a retroactive permit for a cob house that he had already built, had been told by the former chief building official in the department that the permit would never be issued. His replacement is apparently a strong advocate for sustainable solutions and was happy to issue the permit. So sometimes perseverance is the most valuable resource.
Q: I am wondering if building a cob home in the south Texas Gulf of Mexico region would be long lasting and permanent. Also I have two very large piles of concrete in my yard, can I use concrete as my base wall.
A: Cob has been proven to withstand very harsh weather conditions, for example in coastal Britain. You would need to design a cob home to be appropriate for the local climate, ideally using porches, roof overhangs, landscape walls and vegetation to keep the brunt of the weather off of the walls. Lime plaster is also a good idea for exteriors in areas with a lot of storms and wind-driven rains, since they do not get soft when wet, but still allow moisture inside the wall to evaporate out. A bigger concern, depending on your site, could be flooding. Earthen walls can lose their strength if they are saturated with water for a prolonged time. Choose a high site, out of all possibility of flooding, and use a stem wall made of water-resistant material like stone. Recycled concrete chunks can work very well, but concrete is porous and can wick water up into the cob wall, so excellent drainage under and/or around the stemwall is recommended.
Q: I'm from Sri Lanka, a tropical country close to India. I'm interested in building a Cob house and I want to know if it is suitable. We get 6 month of rain and 2 months of extreme wind. The temperature varies from 18 centigrade to 30 centigrade thoughout the year. We already have wattle and daub houses built by villages some time back. The roofs of these houses are built either with straw or with coconut leaves. Iis it possible to build a cob house in this environment? What is the suitable roof shape to stand in a strong windy environment and in rainy season?
A: I have no doubt that a cob house could be built in Sri Lanka. Its durability would depend on many factors, including the quality of the cob mix, the overall design, foundation material and height, drainage, roof design and overhang, and exterior finishes, as well as timely maintenance. An earthen plaster on the exterior of the building will need repairs fairly frequently if it gets hit by a lot of wind-driven rain. Lime plasters are much more durable, though cement-based plasters are not recommended because they can trap moisture inside the wall.
As far as roof shape, the best shape for protecting the walls would have overhangs to protect the earthen walls on all sides. For example, if the house is round, then a conical roof would protect it best. If the house is square or rectangular, then a hipped roof would protect it best. Large extended porch roofs or verandas are excellent for keeping the weather off of the walls, although they can catch a lot of wind, so the roof would have to be tied down strongly. Look around at successful examples of old buildings in your area, and learn from them!
Some other ideas for protecting the building from wind-driven rain: plant large trees close to the building on the side that the wind comes from, or else a sacrificial wall that would take the brunt of the weather and keep it off the house. Maybe you could build the house in the lee of an existing building, grove of trees, hill or other landscape feature. Another option, if the wind comes predictable from one direction, is to use a more weather-resistant material or finish on that side of the building, such as a glass greenhouse, or a concrete wall.
Q: I want to build a straw bale and cob residence in western NC. I get conflicting info about this as some sources say it's too humid here for straw and others say it doesn't matter. My house would be facing northwest on a wooded, sloped lot. I need at least 1200 sq. ft w 2 bdrms/one bath. What do you think?
A: You should be able to successfully build with straw bales in your area provided that:
Your ideas sound fine except for one: "facing northwest." To keep the building comfortable in both the winter and summer, with minimal use of active heating and cooling systems, the building should face approximately south. A northwest-facing building will not receive sun to warm it up in the winter and can easily overheat in the summer as the late afternoon sun enters the building. If your site is too wooded for passive solar heating, I would recommend taking down some trees. Keep in mind that with a typical building, the amount of energy used in heating and cooling over the lifetime of the building is many times higher than all the energy that goes into building materials and construction. So you can't claim to have built an ecologically sensitive house if you don't do everything possible to reduce heating and cooling loads by using passive solar principles.