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 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.