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.

Questions and Answers

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: 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. 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: 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.

Of course, being near a fault line increases the stresses on any kind of building. Cob is more resistant to earthquakes than mud brick, but it is still prone to damage in a large shake. There are a number of things you can do to minimize the risk. One would be to limit the height of the building to a single story. Building on a stable site with a very solid foundation are also critical. And there are a number of other recommendations from there to decrease the likelihood of serious damage to the building or to its inhabitants in the case of an earthquake.

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?

A: 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.

My guess is that you will be very challenged to get permits for either load-bearing cob or a true tree house. If you are determined to get permits, then I'd recommend starting a conversation with your local building department as far ahead of time as you possibly can, as it may take some time for them to become educated enough to feel comfortable with the idea.

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:
1) You erect the roof first, to give you a dry place to store the bales and to get the walls up under cover.
2) You design your home to keep most of the weather off the bale walls: high foundation, low walls with wide roof overhangs, porches or a different wall system on the sides of the building you are most likely to get wind-driven rain from.
3) Protect the exterior of the bales with a thick earthen plaster and a final coat of lime plaster in places where there may be water running down the walls.

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.

Q: I am looking to build a "cob" in Talkeetna, Alaska. I am concerned with insulation. Would a coil of straw (such as those used for wetlands mitigation/management) between the walls suffice? The coil is roughly 8-10 inches in diameter.

A: I would not recommend building a cob residence in Alaska. The issue, as you point out, is insulation. As you know, cob on its own has poor insulation value. There are ways to improve the situation, but I don't know a way to improve cob's insulation value using natural materials to the point where it would be sensible in your climate. I wouldn't recommend embedding straw inside a cob wall; it is likely to rot eventually and be impossible to replace. Even if it didn't, 8-10 inches of straw is still not great insulation for your winter temperatures. Sure, it would be possible to keep the building comfortable by burning a lot of fuel; but we need to be reducing carbon emissions by burning less. If you're going to live in a place like Alaska in the winter, a well-insulated building is the only environmentally responsible choice. If I were in your place I would be considering a straw bale wall system of my house.

Q: I am in the process of purchasing land in Squaw Valley, CA and would love to build a cob home. There is lots of hay, sand, and trees in the area. My only concern is permit rules because it is CA, however the area is rural. Do you believe I would be able to have a cob home or should I look for another area in CA?

A: There is no code for cob anywhere in California, nor anywhere in the US, for that matter. Some California counties (Humboldt, Mendocino, and a few others) offer a special class of permits to owner-builders, in which structural requirements are relaxed. I don't know about your county, but you can call the building department and ask. Other than that, if you want to build a cob house with a permit you will have to use the Alternative Materials and Methods provision in the building code. This clause allows building officials to permit materials and systems not in the code if they are convinced that they are safe. In practice this generally means that you will need to hire a state-licensed structural engineer familiar with cob to sign off on your plans. The general attitude of your building department and the specific interests of individual inspectors will make a big difference in how smoothly this process goes. I would recommend asking around about other people's experiences with the building department in your county. You could also ask the building dept. whether they have permitted any straw bale or other "alternative" structures, and, if so, what those experiences were like.

Q: I am hearing that cob is difficult in Hawaii, although I was hoping that wasn't the case.

A: The complicating factor on some of the islands is lack of clay. As I understand it, the Big Island has simply not been around long enough for clay to form. If that's the case, it would remove cob and most other earthen building techniques from the picture. I know there is plenty of clay on Kauai, and perhaps some of the other older islands, and I have also heard reports that some of the volcanic soils on the Big Island are adhesive in some way and can be used for cob. In the absence of clear information, I would recommend that you read a book ("The Hand-Sculpted House"), and/or take a class, and experiment for yourself.

If clay is not available where you are, other options I would consider are building with lava rock (an ancient building material still in use today) or earthbags, which is one of the few earth building systems that can be done successfully without clay.

Q: We want to build a cob house instead of the mobile home we are in. We live in Bainbridge, GA where humidity is very high and we also have a lot of rainfall. It would be the first in this county to be built so we are going it alone. We are a family of disabled people, but we need something better than this home that is falling apart. Can you give any pointers of how we should start this project.

A: When building where you don't have a dependable dry season, the best approach is to get the roof up first. This can be supported either on temporary posts which will be removed once the cob walls get up to full height, or on a permanent post and beam structure. I strongly recommend taking a workshop if you have never built with cob before. There are good teachers not to far away, in Tennessee (barefoot builder) and North Carolina (Ashevillage institute) if not in Georgia. Another good first step would be to read "The Hand-Sculpted House."

Q: I'm a student from the Philippines who is quite fascinated with Cob houses. We experience tons of typhoons, earthquakes, and other calamities each year. With that said, what can you recommend if I'm gonna build a Cob house considering the fact that my house is pretty much susceptible to these forces of nature? Should there be any specific design on the structure?

A: It's difficult to offer a prescription every possible calamity in a few words. Earthquakes and high winds have some factors in common and others that are different. And of course it's nearly impossible to make a building that will withstand every imaginable force of nature. However, here are a few general principles that should serve you well:

1) Build small; single story with a lightweight roof.

2) Build a very strong foundation, and anchor both the walls and roof strongly to the foundation. Reinforced concrete is the best foundation system for resisting earthquake damage.

3) Minimize the size of openings (windows and doors) and leave plenty of cob between them.

4) A reinforced concrete bond beam at the top of the wall will help tie the walls together and provide a strong anchor point for the roof structure.

5) To protect the cob walls from wind-driven rain, a veranda or wraparound porch is a good idea. However, this could tend to catch the wind in a big storm so it will have to be very strongly built and well anchored.

6) Observe how other people build in your area and which types of construction survive calamities best. Mimic successful practices.

Q: I will be building in southeast Ohio we have hot summers and mildly cold winters with average rainfall of around 3.5 inches a month with relatively high humidity. I want to incorporate a green house on the south side of my cob home that will have three glass walls with the southern exterior wall of the home acting as the back wall of the greenhouse. I am wondering if the added humidity in the greenhouse will effect the adjoining wall. I do intend to let the cob walls dry completely before adding the greenhouse.

A: The moist air from the greenhouse shouldn't have any adverse effect on the cob. I have built or seen several greenhouses attached to cob buildings in the manner you describe. If you're going to be spraying a lot of water in the greenhouse to irrigate plants, you may want to use a water-resistant finish such as a lime-sand plaster.

Q: My wife and I want to build a house sometime in the near future that is energy efficient, sustainable, and possibly off-grid. We like the look of cob, but can you tell us if cob architecture will hold up to the climate of northern Kentucky? With the amount of rain and snowfall we get, would it hold up?

A: A properly designed and detailed cob house will have no problem holding up with your weather. There are cob houses on the coast of Ireland and Wales that have been blasted by North Atlantic gales for 500 years and are still in fine condition. Of course they've been maintained and repaired as necessary. There are also cob homes in Denmark, New York (dating back to the 1800's) and many other cold, damp places. There are considerations to making an earthen building durable in such a place, such as a high waterproof foundation, wide roof overhangs, and good detailing around windows and doors to keep water out of the walls. You can read about these and other recommendations in "The Hand-Sculpted House" by Evans, Smith, and Smiley.

Just because a cob building will be durable in your climate doesn't necessarily make it your best choice. Cob walls are poor insulators. Especially where winters are both cold and cloudy, I would recommend making the exterior walls of your house out of something with better insulating properties, such as straw bales, straw-clay, or woodchip-clay. "The Art of Natural Building" by Kennedy, Smith and Wanek is an excellent introduction to all of the options for natural homes which will help you select which ones might be most suitable in your situation.

Q: I have wanted to build an earth friendly and healthy home for decades. Now that my husband is retiring and our constant moving is coming to an end, we are about to purchase land in the Asheville, NC area. While living in dry Arizona, I was sold on straw bale construction. Then a little over a decade later, living in warm and moist South Carolina, I changed my mind to Cob construction. Now that it looks as if we will be moving to a slightly cooler, yet still moist climate, I don't know what to do! What would you recommend? It would have to be a relatively contemporary/traditional looking home as my husband says he is not willing to go full "mountain man."

A: I think either cob or straw bale or a combination of both could be appropriate in the Asheville area, as would other natural wall systems such as straw-clay or woodchip-clay, which might be easier to make look "contemporary.". There are some good local resources who you could consult for more suggestions. I would start with Earthaven Ecovillage (www.earthaven.org). Local experts will be able to share their experiences of what works best in your climate and bioregion.

Q: I'm currently in the military, and am saving money as I'm able so I can buy land and build a cob house. I want a small semi-sufficient homestead with some animals and garden, for my family and generations to come. But I think the first step is deciding where it will be and buying the land. After that I can work on the site development. What I want guidance on is choosing the right land, in terms of climate, proximity to natural resources, fertility, etc. What are some resources I can use to help find the right land?

A: This is a tough question. There are so many factors to consider when choosing land. In addition to the ones you mentioned I would add price of land, access to public transportation, markets or jobs (depending on what your income source will be), and cultural issues such as building regulations and supportive neighbors. In many parts of the US, building a cob house legally is difficult and expensive, but there are still rural areas with no building codes. Also, if you want to do something out of the box like building a cob house, you’ll be much more comfortable if you can do that in a supportive community. What about the location of family and friends? Homesteading and building a house are very difficult to do on your own; I would think about where you have or can find a supportive community to help out.

So I would start out by choosing a region based on real estate price, climate, and social/cultural factors. Then make a list of the most important features of the land itself based on what you intend to do there. For example, how important is flat, fertile soil for what you want to do? Irrigation water? Cell phone service? Even though you will doubtless have a long list, I would suggest choosing your top 4 priorities since there’s little chance you will find everything you want. Then you can hand your list to real estate agents in the area you’ve chosen.

Have you studied permaculture design? If not, I’d recommend it as a way to think about designing your homestead. Permaculture design is usually taught in 2-week residential workshops. You could do an internet search for a workshop, which will also be a great place to connect with peers who have similar interests. Maybe when you have time off or after you get out of the military.

Q: We want to build a cob home some where but are having trouble picking a state. What states can you actually have a cob home in and let us know what to watch out for weather wise?

A: Unfortunately, this is not a simple question. Building regulations are typically administered by local jurisdictions such as counties and cities, rather than by states, and can vary widely within a state. There are some rural areas of the country where a building permit is not even required (whereas urban areas in the same states likely have stringent building regulations). I know of such permit-free locations in Missouri, Maine and New Mexico, but I’m sure there are many others. Other areas, including several counties in California, have owner-builder codes that relax building regulations when people are building for themselves. Where regular building permits are required, it may still be possible to build a cob home legally using a provision in the code called “Alternative Methods and Materials.” For example, a small cob building was recently permitted in Berkeley, CA using that provision. This typically requires the services of a state licensed architect or engineer. The situation should soon get much better everywhere because a cob appendix has just been accepted into the 2021 International Residential Code, a model code used as a template most places in the US. You can learn more about this development here: https://www.cobcode.org/code-approved It also bears mentioning that even in places where building permits are technically required, many people choose to build without them. This is potentially risky, usually if a neighbor decides to report the unpermitted building to the authorities. But it can work out if you have a very secluded building site and/or excellent neighbor relations.

Cob is a high thermal mass material with poor insulation value. If you want all of the walls of your home to be made of cob, that will only be energy-efficient in a place where the daily temperature cycle usually stays within a comfortable range. For example, in high desert locations where, even when the daytime temperatures are very hot (over 100°) the nighttime temperatures are cool (say, 60°). Even in these locations, wintertime temperatures are colder than ideal, but as long as there is ample winter sunshine you can go a long way towards heating your home with passive solar design. Another good location is along the California coast, where the weather never gets too hot or too cold. In most other parts of the country, I would recommend using a higher-insulating wall system such as straw bale for most of your exterior walls. I would not recommend building a cob home anywhere with very cold winters. In a location where daytime temperatures sometimes stay below freezing (all of the northern, midwestern, and northeastern states) you will simply lose too much heat through your poorly-insulated walls for cob to make any sense as a wall system. Any environmental benefits you have gained by using a low-embodied-energy building system such as cob will be lost many times over by the ongoing need to expend excessive energy heating an inefficient building. There are some projects underway to learn how to insulate cob using combinations of mineral binder and plant fiber, such as hempcrete and straw-clay. Within a couple of years, we may know how to do that effectively.

Q: I have a 40 x 60 x 22 (height) hay storage shed. The structure is very solid. I would like to use the structure as a frame for a 2 story COB Home. I like the thickness of the COB walls for insulation and ease of keeping that type of structure cool and easy to heat in the winters. Does using a structure like my hay barn provide a good structural foundation for COB built walls inside and out?

A: It’s hard to give you any precise answers without knowing a lot more about the structure and where you are located. Cob walls actually have a very poor insulation value and excellent thermal mass. If you live somewhere where the weather is fairly mild year-round, cob can be a good choice for exterior walls. If you live where winters get very cold and/or summers get very hot, you should consider using a better-insulating wall system (such as straw bale or light straw-clay, for example) for your exterior walls. Cob can still be appropriate for interior partitions, built-in furniture, etc.

Q; I'm planning on building a home in the Republic of Georgia where it's extremely rainy, 42% of the days of the year have precipitation. I've seen that in Britain, an equally wet climate, they have cob houses with thatch roofs that have lasted hundreds of years and thus I think I can build an earthbag or cob structure if it has adequate roofing, waterproof plastering, and protection from ground water. Could you please direct me towards any resources specifically geared towards a wet and potentially frigid winter climate? Am I completely out of my mind in pursuing this or is there still a chance I can construct a natural building home in such a climate?

A: I have little doubt that if you can build a natural home in your climate, with proper design and construction detailing, that it will survive fine in your climate conditions. The difficulty is going to be getting it built. Do you have a reliable dry period? If you don’t you will most likely want to put your roof up first and then build walls up to it. I do not recommend building your exterior walls out of cob in your climate without additional insulation. The same goes for earth bag unless you have some kind of very light and insulating fill material for the bags. There are some exciting ideas about insulting cob with natural materials (especially the CobBauge project from the UK and France). But if you don’t have a reliable dry season, cob will be very difficult to build. I would probably recommend something like straw-clay or hemp-lime, which are insulating infill systems within a timber frame. The best resource I know on how to design and build high-performance natural buildings in extreme climates is “The Natural Building Companion” by Jacob Racusin and Ace McArleton. It’s an expensive book, but well worth the investment in your situation.

Q: I am interested in purchasing land and building in NorthWestern Pennsylvania very close to the Ohio border. How doable is this in this area? The home has to be a minimum of 900square feet. 

A: I’ve broken your question down into 4 questions I think you might be asking, and attempted to answer them.

1) Are the materials I would need to build a cob house available in my area?

Probably. You will have to test your soils to see whether they are suitable for cob construction and, if not, find an alternate source. “The Hand-Sculpted House” walks you through this process.

2) Is the expertise I need to build a cob house available in my area?

I don’t know, but it may be difficult to find professional designers and contractors in your region with cob expertise. You will likely need to educate yourself and/or the professionals you work with. There’s a new book coming out, “Essential Cob Construction” that is intended for exactly this purpose: https://newsociety.com/books/e/essential-cob-construction. This book should answer all of your questions.

3) Is the legal/regulatory climate amenable to getting a permit for a cob home in my area?

I don’t know. Every building department is different in their openness to non-standard designs and materials. In order to get a permit, you may have to hire a licensed architect and/or engineer. The new model building code (Appendix AU of the International Residential Code) should make it much easier to use the Alternative Materials and Methods provision of the code. Learn more at www.cobcode.org

4) Is cob a suitable choice for my climate?

In order to get a building permit for a cob home, you will likely have to demonstrate compliance with energy efficiency standards. Cob walls have relatively low insulation values. You will most likely have to add a more insulating material (such as hempcrete or light straw clay) to the outside of your cob walls - or use a better-insulating material (such as straw bale) for your exterior walls and restrict cob to interior partitions and sculptural elements. It’s also good to know that the nature of your cob mix has a big impact on its thermal performance. Lightweight cob mixes with less sand, a great deal of straw, and/or lightweight aggregate such as pumice have much better insulation value than standard high-density cob. But even so you may still need additional insulation. Even if you do not intend to get a building permit, you still probably want to design an energy-efficient home to reduce long-term economic costs and environmental impacts. There’s a lot more information on this issue in “Essential Cob Construction."

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