Green Home Building: Where does cob work?

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.

Q: We desperately want to build a cob home. We are getting on in age and do not need a large conventional house. Cob seems to be the perfect alternative, small, compact and cozy. We have been trying to find out if there are any counties in our area that allow cob construction. We currently live in North Carolina. But would be willing to relocate to South Carolina, or Virginia if we could find a place that would allow cob construction. Do you have any information on areas that allow cob construction, or any information on where we can find out what areas do allow cob construction.

A: There is no cob code per se anywhere in the U.S., which makes it challenging to get a permit for a cob home. However, people have nonetheless acquired building permits for cob homes in various states. Many more people have built cob homes without permits. Some have had legal problems but many have not. Most building codes include provisions for "alternative methods and materials" not specified by the code. In most cases, the use of this provision requires the involvement of a state-licensed architect or engineer to sign off on your plans to ensure that your building will be safe.

If you decide to pursue a permit for a cob home, the best approach would be to be very direct and up-front with your local building department, tell them about your plans and why a cob home is important to you, and ask them what they would need to give you a permit. It's good to educate yourself as much as possible before having this conversation. For example, you could get documentation from other permitted cob homes in your state or as nearby as possible.

You have some great resources available in North Carolina. One is a group called Kleiwerks (www.kleiwerks.com) based in Asheville. They are a great resource on cob and other natural building techniques in your part of the country. Another North Carolina resource is Clarke Snell of www.thinkgreenbuilding.com. These contacts should be able to provide you with the help you need locally or get you in touch with people who can.

Q: I live in Indiana where the humidity reaches near 90% in the worst parts of the summer. We have colder winters with temperatures reaching down into the teens and pretty warm summers with temperatures mostly in the 80s but sometimes reaching the mid 90s. Rainfall averages are at the highest near 4" in a month. Is cob a good choice for our location?

A: Cob is a very good material for passive cooling of buildings, especially where night-time temperatures drop far enough to discharge the heat built up in the thermal mass during the day. If your summer humidity is that high, your nights are probably warm. In that case you will probably need to augment cooling with a swamp cooler or the like.

Cob has poor insulation, so is not an ideal choice for exterior walls where winters are cold. If you have good winter sun when temperatures are at their coldest, it could still work out as a reasonable option. Otherwise I would recommend using a better-insulating material such as straw bale or light straw-clay for your exterior walls and use cob for interior walls and built-in furniture for temperature moderation.

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'm really interested to have a cob house of our own.Do you know somebody in the philippines who can train and help us build one earth friendly home.

A: Not knowing anything about the status of natural building instruction in the Philippines, I sent along your request to my colleague Tim Reith of Seven Generations Natural Builders. Tim works a lot in the Pacific, and he had this to say:

I don't know of any builder-instructors in the Philippines. The closest locations that I can think of are mainland Southeast Asia: Thailand has numerous local and visiting instructors and courses nearly across the country; Laos and Cambodia also have burgeoning building communities (cross-pollination from Thailand primarily). Further afield would be Australia and Hawaii. That said, the Philippines have thousands of years old pottery traditions (many communities still make ceramics, so people know how to work with clay) and plenty o' clay sediment, volcanic sands, and rice straw.
Without immediate instruction or the ability to travel for a course, this may be a great opportunity to purchase The Hand-Sculpted House and other cob books and begin experimenting and building w/ cyber support through the GreenHomeBuilder website and the coblist, etc.

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: Can You build a cob structure in southern Florida or any part of Florida for that matter, considering the earth is very sandy and the water table very high? I live in southern Florida where it has a lengthy rainy season. It doesn't seem feasible for building with cob let alone sustaining a structure made of cob considering the soil, climate and other seemingly non-conducive conditions.

A: I have no doubt that you could build with cob in southern Florida if that is what you really want to do. There are examples of cob buildings in rainy wet tropical locations. I agree that the weather and soil sound like major complicating factors. You would probably want to build a temporary roof or string a tarp over the site to protect the cob walls from rain during construction, and the slow drying time would make cob building slow. You might also have to import clay to add to your soil to get the proper mix. And you would need to be very thoughtful about site drainage to prevent groundwater from infiltrating your building. Given all of these factors, cob may not be the most logical choice for your locale. What do you know about pre-industrial building systems in your region? It's always instructive to do a little historical research to find out what has worked in a place in the past.

Q: I live in central Minnesota and I was wondering whether or not cob would be the best material for a summer cabin. The climate here is humid and hot during the summer with Siberianesque temperatures in the winter. The only problem with this cabin is that we have no way to heat the cabin during the winter short of driving ten hours every day to put wood in the furnace. My question is: Will the cabin crack apart during the winter if left unheated? The temperature ranges from 40 degrees Fahrenheit to -40 degrees Fahrenheit.

A: There is no reason why cold temperatures alone should damage a cob building any more than they would damage any other building type. The only concern is if you have a leaky roof or a plumbing failure and water soaks into the walls and then freezes. This could cause damage to the cob walls, just as it would to any other kind of wall. There are examples of cob buildings standing for centuries in northern European countries such as Denmark, so freezing temperatures alone are clearly not a problem. A bigger problem for you might be getting the cob walls to dry during your humid summer weather, but I'm sure it is possible to do with some experimentation.

Q: In the Q and A you keep saying that cob is not suitable for very cold climates, but that there are cob homes several hundred years old in some very cold climates. How did this work out? What are the traditional methods (not adding strawbales, I don't think they had those back then) for making a cob home livable in a colder climate? Also, what do you do about areas such as bathrooms that will be wet? We are looking into using some sort of green house in OK which is not an extremely cold climate but can have freezing temperatures at night for several months and sometimes during the day for a few days at a time. I am leaning towards cob because it seems to be easier to build yourself and therefore cheaper. We don't have to deal with codes so we can do whatever we want.

A: Cob buildings will survive fine in very cold weather. However, like stone, cob is a poor insulator and is therefore not the most efficient choice for cold climates. To keep it comfortable in the winter you would have to input a lot of supplementary heat, unless you have very dependable winter sun. Traditionally people had few choices about what to build with and were probably used to cold homes in winter and to constant heating and cooking fires. Today we have more choices about how to build, and the carbon pollution from constantly burning wood should be avoided.

Cob can absorb a lot of moisture without a problem. If there is going to be a lot of water getting on the wall, use a water-resistant lime plaster. But except for walls that have water getting on them directly (such as those around tubs, showers, sinks) there is nothing special you need to do. A cob greenhouse sounds like an excellent place to start.

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: I'd like to know if the greater Houston area has zoning laws agreeable to cob houses.

A: The regulations you need to find out about are building regulations, not zoning. I don't know anything about permitting earthen buildings in the Houston area. You could either contact your building department and ask them directly, or else try to find other builders in your area who have built non-conventional structures and ask them about their experiences. One group I know of that has experience with cob buildings in Texas is called Barefoot Builder. Check out their web site at www.barefootbuilder.com.

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 was wondering if you know anything about building permits for British Columbia for cob homes? I connected with our local building inspector and he laughed at us and said that cob homes are for people who don't know how to build homes. He said that he highly does not recommend building with cob and basically told us that we a stupid and ended the conversation. We didn't get any answers, he was rude. I want to know what the permits are. We don't want to build a home without them because we don't want to risk anyone finding out and making us tear it down. Do have any advice into which direction we should be heading in to complete our goal of building a cob home?

A: Sounds like you had a very unpleasant experience with your local building official. Unfortunately, local officials have a lot of power over the ease with which non-standard building projects are permitted. I don't know the specifics of the codes or permitting process in your area, but I do know that cob buildings have been permitted in BC. It would probably be very helpful if you can find someone fairly local who has successfully navigated the permitting process. I recommend contacting your local (provincial) cob building experts at www.cobworks.com. Good luck!

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.

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