Cob Building is Not Appropriate For This Cold Climate

by ziggy on March 3, 2011 -- 22 comments -- Follow

There’s something I’ve had to come to terms with living in Gobcobatron. That is that cob is not the most appropriate, responsible building style for this cold, wintry climate of northeastern Missouri. I think this applies to similarly cold climates as well. Sad to say, but it’s the reality, I think.

Here are my thoughts on the matter.

Cob House Cold Climate


Cob is Not Insulative

Let’s get this out at the forefront: applying an R-value (insulation value) to cob doesn’t even make sense — it doesn’t register. It is not an insulative material — it is massive. And by the way, thick walls do NOT automatically equal warmth or insulation. Cob itself will never be insulative. Massive walls want to conform to the ambient air temperature, and if it’s 25 degrees for a week, that’s what those walls will want to be. An earthen wall does not buffer against temperature shifts the same way an insulative wall does.

In essence, my cob house (Gobcobatron) has essentially zero insulation. The roof, if you don’t count the soil (which I think it quite fair), does not have insulation, nor does the floor, nor the foundation. The walls are straight cob. It is pure mass from floor to ceiling. However, that does not mean that a cob house can’t be built without insulation.

You can include insulation in an all-cob house in the floor, foundation, and roof. So wouldn’t that give cob houses more of an edge in a cold climate? Sure. As would including a greenhouse. But I am still very doubtful that cob is actually a responsible building material in locations with cold, cloudy winters. As a note, where I am located (northeastern Missouri) is USDA planting zone 5, with max winter lows clocking in at -20º. Although that is not common, it’s possible. Our average low temperatures in the coldest months hover between 10-20º.

Heating a Cold Cob House = Heating a Fridge

Even with insulation in the floor, roof, and foundation, heating a cob house is a constant battle against cold outdoor temperatures. The mass is totally exposed to ambient cold air temperatures more than it is exposed to warm indoor air. There is a great imbalance. It’s like trying to heat a refrigerator – the cob wants to be cold because that is what it is most exposed to. (Think of all of that surface area of the exterior face of the walls!) To make matters worse, if winter days are frequently cloudy (as they are here), the cob will have little exposure to the warming sun and will stay cold. All this means is that you’re not going to be warm without firing a wood stove very regularly (likely, constantly).

Yes, passive solar design helps, but it only really helps if you have insulation in your walls to slow down the transfer of heat/cold. You won’t really be capturing heat because the walls/floor are so cold to begin with that the sun will only perhaps prevent temperatures from dropping further. And again, if it’s cloudy half the time, the sun will only be able to work with you half the time to warm your home!

Plain and simple: heating a cob house in a cold climate with insufficient sun takes too much wood to be considered really ecologically responsible. My original theory was that building my home with as little embodied energy as possible in the first place would give me something of an edge as far as the total energy required to build and then maintain the building. I think that is perhaps flawed thinking. Using little embodied energy in construction is crucial, yes, but I think you can still do that AND create a building that requires less energy during its lifetime of usage.

Cold and Condensation

There’s another fun issue, too. Condensation is a major concern in situations where you have warm air hitting a cold surface. In this case, warm air generated by a wood stove that makes contact with cold walls is an extremely favorable situation for condensation to collect. We have suffered greatly from condensation issues in two of our winters living in Gobcobatron. The walls on the north and west, just above the foundation registered as low as 35 degrees Fahrenheit most of the time! As we generated warm air with the wood stove, moisture formed on the surface of the wall, and because it was so damp, it never had opportunity to dry out. Then the mold came in… and needed to constantly be wiped down with vinegar. That is not a healthy living situation by any stretch of the imagination.

Cob = Not For Cold Climates

It just doesn’t make much sense. Cob is better suited to mild climates, where it rarely (if ever) freezes, and places with adequate sunshine in the wintertime. Northeast Missouri is not that place. I advise against building with 100% cob in places such as here from now on.

That doesn’t mean I don’t love cob, though. Damn I do love it. But it’s a reality check — there are better choices for building in cold climates. Straw bale is a much wiser choice, for example. You’ll be burning a lot less wood during your building’s lifetime if you have adequate insulation, and you’ll be able to maintain a healthy living environment free from condensation, moisture, and mold, too.

(Updated: 10/2013)

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  • emidio

    do you have plans to update your house to fare better in the winter? you mention insulating the floor, foundation, and roof, but not walls–have you considered insulating the walls? also, out of curiosity, at what temperatures do you keep your house during the day/night, and how much wood is required to do so?

  • Kyle

    I’m new to the world of eco-living and am attempting to learn as much as possible, so forgive me if this question is one with an obvious answer.

    What building materials/styles would you recommend for colder climates then, if cob doesn’t seem to be the ideal choice?

  • neon

    I am not an expert, but I don’t get it. Any building material has some heat conduction. The question is, if you use appropriate materials for your climate. There are no miracles, or are there? What other option could you suggest, that would provide you with much better results? As I understand it, cob is very cheap, insulation from straw bales is very cheap. Usually, there’s much more straw insulation layer than the cob layers. The problem is, to use enough insulating material to overcome the problems of the cold walls. And that you need to burn a lot of wood? I can’t imagine other scenario, if you have such cold weather. In short, I don’t understand, why should there be any significant difference in other building materials. You need mass (cob), you need enough insulation (straw), insulated all sides of the house and the heat you will generate inside, won’t so easily escape from the heated mass of the cob, if you have for example 0.5 meter of straw layer. Your house is a good experience, but it seems to me a little bit naive, to expect miracles. If I would be at your place, I would surround the walls with straw bales and add another cob layer on them. The heat generated inside won’t escape so easily. Just imagine the thick layer of straw from outside. This is what I call miracle – straw bales are very cheap and they do perfect job.

  • Neon: As you yourself realize, you need some amount of insulation and thermal mass, but skewed too much in either direction is not a good thing. And this house is skewed way too heavily in the thermal mass arena. Like I said, the house has zero insulation. Even an all-cob house with an insulated floor, roof, and foundation, I think, would not be sufficient for this climate, either, as I stated above.

    A more appropriate home for this region might be bale-cob, or certainly straw bale. (As for bale-cob… I’m not sure if all that thermal mass is really necessary? I don’t have too much experience with it, really, but I wonder if 6″ of cob is really necessary…? Might the thick plaster on a straw bale be sufficient for thermal mass?)

    Anyway, straw bale homes are pretty successful in this climate. That would be my choice for a future home. Our kitchen which is under construction right now will be bale-cob.

  • hallie

    Straw bale was the first thing I thought of, too. It would be fun to try a ‘test’ (non-living-quarters) structure with it and see how you like it.

    Cob does quite well in Oregon, but our winters are relatively very mild. Of course, wood-framed apartment buildings (like this one I’m in now) with poor insulation also feel cold when the bitter north wind kicks up and it’s dry and cold – something that doesn’t happen here often. In that case, I’d be praying myself for three-foot-wide walls of straw, or any insulation.

    Not all earth-sheltered buildings are as exposed as yours, though. Siting is everything. If you could have built into a hill with just a cob wall facing southeast to seal you off from what was essentially an earth-sheltered cave, that may have worked much better. Nothing is foolproof, certainly, but some sites are better than others at protecting you from prevailing conditions.

    Cob-bale should be good; I’m interested to see how it turns out.

  • Stephen

    I love your blog. I’ve been interested in cob building for more than a few years now. Reading your blog has made me lean more towards strawbale though, with cob accents and features on the inside. I hope you keep this blog going. It’s too bad that your cob house didn’t turn out the way you would have liked. You might invest in a strawbale home.

  • due zingare

    maybe the greenhouse all around the house would be sufficient?
    ..we lived in a narrowboat for years, (steel in water, with 1/4 inch plywood inside)and the stove, just like yours, was on 24/7 from nov to apr…it used coal and was not a great expence, because of the small area. it was warm and easy to manage.
    we now have an old cob house to fix, and we agree that it is daunting..everybody we know is busy felling/coppicing/buying enormous amounts of wood, or paying tons for gas/oil..italy, where we are, doesn’t use coal.
    if given a choice, we’d prefer stawbale for the winter, but it wouldn’t be cooler in the summer…maybe the ideal is a extension to the house in strawbales, as winter quarters, leaving the cob for easy summertime living~

  • I live on Vancouver Island, roughly USDA zone 8. While we don’t have the freezing cold winters you do, we have very little sun during the winter and we also have lots of rain and humidity. I have been studying cob and other natural building techniques and I live in an area where there are several cob buildings, one of which was built using a grant and they installed humidity and temperature monitors within the walls to study it over time.

    What they do here is this: first, nobody builds without insulation and our climate would be considered mild compared to yours. second, the cob walls are thick, 12 -20 inches. third, north facing walls are done with straw bale for the added insulation. However, due to our high humidity the straw bale is covered on each side with a layer of 4 inch cob. finally, every cob home here is heated with radiant in-floor heating, with wood stoves as backup or just for added ambience. The in-floor heating distributes the heat throughout the floor, which rises up and warms the air more effectively.

    I have only just discovered your blog and am in awe of your determination and willingness to “go for it”. What an incredible learning experience for you! Looking forward to reading through the archives.

  • Hi Ziggy,

    I have been a faithful follower of you blog since day one!
    It is a shame that you are having all these problems with your house, however it seems a little too much stating that cob building is not appropriate for cold climates like the one you are living in.
    I do appreciate all your effort and determination, but surely you knew that cob along would not make any miracles. Perhaps you should say instead that an all-cob house with no insulation (either on foundations, walls, roof or floor) and single glazing are not appropriate for harsh winters… Earth is an excellent material for construction, but you still need to follow the good practice rules if you want to live thermally comfortable, and the sane applies to all building materials!
    You could even say the same for hot climates. Take the following example:
    Imagine you are building a cob house in Mali, where it can get really hot, and you decide to have enormous single glazed windows facing the sun, with no shading elements. To this add the fact that you had not thought of a ventilation strategy for the house. The huge amounts of solar gain would overheat the house in no time, which would of course make it extremely uncomfortable to live in. Does this mean that the material is not appropriate for the region? No, it just says that you were not respecting what the climate demands. My point is that more than the material you have to consider the design of the building, according to its climatic context. Poor design will eventually lead to a very poor performance.

    Your experiment has great value, specially because you inspired people with your creative attitude and impressive determination, however, building-wise it was slightly naive…
    Don’t give up on cob, just use it properly. Hopefully you will be able to learn from your mistakes and plan your next house so that they won’t happen again. Good luck!

  • ziggy – i’ve been thinking of building into the southern-facing slope of the spot i lived at before at red earth. how would you approach a partially earth-sheltered home with your current knowledge/experience with cob?

  • Joan: not sure. I don’t know that much about earth-sheltering. All I can say is: drainage!

  • Eva Elisabeth

    Love your blog, thank you for the honest assessment. My Mom adores the idea of a cob cottage but moving to Minnesota I think that Straw Bale will be our best bet, we can always have interior cob walls for that curvy feel 🙂 Keep on keeping on and good luck with all your new endeavors.

  • Dan@EC&D

    Ziggy, we all come to the realization that sometimes our clean vision has some flaws. I would encourage you to NEVER give up NEVER surrender! Yes your cob style construction has issues or should we say the location and climate thereof does but this is the mother of invention or ingenuity. I initially (and still are) an excited follower of Rammed Earth for many of the same reasons you are interested in your cob construction and ran into the same issues here in the Midwest. This did make me come up with a good solution; I would also say you need to consider insulating the exterior NOT the interior side of your cob. The effect should give you what you need far easier! I look forward to hearing more about where, what and how your moving forward.
    “A single strand is easily broken, but a cord will withstand the challenge!”

  • Hi Ziggy,
    Thanks for sharing your story.
    I’ll have to agree with you that cob is not a cold climate material ( alone ). Old adobes around here in NM, which are also subject to periodic -20º F temps, are c-c-cold in the winter.
    Actually, it can be that way well into the spring. The battery will hold what it is given.
    Makes me think about the double wall adobes, for those that like the geological material of earth, yet want some insulation. Double walls have a thermal break, of air, or pumice or something(?) between the walls. Though, the foundation for such a wall would be massive!

    I Love Cob too! I’m polyamorous when it comes to natural building materials. We just have to be aware of their personality traits to build a good relationship.

    Insulation on the outside. Mass on the inside.


  • coblearner

    Hey, thanks for sharing. makes sense. dude, it sucks to be cold. i hate being cold. rocket mass heater or not.. when only 10-20% mass of your cob is radiating heat vs. 80-90 percent radiating cold.. it’s a losing battle.. heat rises.. how much problems did you have with condensation?

    btw. did I mention I hate the cold. .. i hear strawbale is awesome at insulation.. just your footprint will be bigger. but.. efficient.

    cob on.

  • rebecca

    dude, when u say 10-20 degrees in the wintertime, are you talking degrees or Fahrenheit? im looking to build in new zealand, we get cold winters but not like, massively freezing, so i was confused about the temps where you are?
    thanks bro, gonna get me a copy of your book- looks choice:)

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  • michelle

    and so r u saying that this isn’t a good idea for us in Illinois??? :((((((
    please email

  • Yup, skip the cob in Illinois, please. You should look into something like straw bale, instead. IL is too cold for an uninsulated home.

  • Cat Weekly

    Hi, Love your articles. I hope to build my own home using cob and straw bale to avoid the heat transfer problem that you’re having. I’ve spent a lot of time researching it and decided the best way to go is straw bale outer walls with cob inner walls. This way the cob works great as mass and the straw bale walls provide the needed thermal barrier. You could do a retrofit on your place with straw bale, for this winter even stacking hay bales around your place–elevate and cover to keep off the rain– will help with the chills. Ugly? Yep, but its better then frostbite. Just an off the top of my head suggestion. Start using the hay in the early spring before grass is really growing and you still need to feed the critters. Cat Weekly

  • Hi Cat: Thanks for the comment. Where are you located? You’re onto a good thought there with using cob strictly as an interior feature.

    I heard recently that someone literally cut bales in half with a band saw, and then stuck the half bales to a brick wall with clay… (amazingly, they stayed put). Later, the wall was plastered. The advantage here was that the wall now had an extra insulation boost, without a full-on stemwall. Weird, but whatever works!

    We are happy to call our cob house a 3 season dwelling, and leave it at that. It performs fine during the spring, summer, and fall… it makes more sense to us to do this, instead of try a weird band-aid solution.

  • Steve

    Ziggy, thank you so much for the information. I’ve been surfing cob building web sites and reading books on this for over a year and have never seen this issue addressed so fully. They always put in the comments about placement and observing the building site, but you’re conclusion that it’s not suitable for cold/cloudy climates is something that needs to be known right from the start. I haven’t read your whole blog but couldn’t help wondering if you had taken a cob building workshop and if they didn’t address it’s suitability for your climate zone. I only ask because, like I said, I’ve never seen it mentioned before and haven’t taken a workshop myself, though I’ve been planning to.
    I’m sorry for your troubles, but thank you again for saving me and probably many others from wasting any more time on the idea of cob in this kind of cold. I live in Northwest Indiana with a climate slightly colder than yours and will be looking more into straw bale now.

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