1: I intend to build a cob house with living space enough for myself, my wife, and our two children.
2: I've read now several books and virtually everything I can find on the web about cob/cob building.
3: I have never built a cob structure, but I have made numerous test bricks with a variety of materials. The test brick made from the mix I plan to use took more than a dozen whacks from a claw hammer to completely bifurcate it. It was about three inches thick and maybe six inches square, and this was after it sat outside in the rain for two days. (I did of course let it dry back out.)
4: I am fortunate to have an abundance of clay and sand on hand, as well as a enough salvage lumber (mostly oak beams/rafters/joists etc) and other materials to use in the roof or other parts of the structure (door/window frames etc)
5: Foundation stone is abundant. Again, much of this is salvage stone from buildings that were constructed at or around the turn of the century. The buildings were/are falling down, but the piled stone foundations beneath them are screaming at me "rearrange me and cover me in cob!"
6: I have a site chosen where building codes are irrelevant, with good drainage, and and other positive factors that don't really warrant a lengthy detailing at this time.
So, while accepting that I still have much to learn I don't necessarily feel like I have no idea what I'm doing. In fact, I'm to the point now where I am getting pretty anxious about building some larger test models (probably a tool shed with a door and at least a couple south facing windows.)
But here's my problem: Warmth.
I live in south western Missouri. Summers are hot and very humid. Winters are cold (dipping often into the teens with single digit temps not at all uncommon) and equally humid. Precipitation is common year round. Now, I realize that cob construction has been going on for hundreds of years in various locales around the world and that stories of centuries old cob buildings in wales and elsewhere can easily be unearthed via google. I also happen to know that during the medieval ages people sometimes froze to death in their homes sitting next to the hearth.
Look, what we live in now is a trailer house that was manufactured in the sixties with virtually no insulation left in the walls, floor, or ceiling, and it is costing us a fortune to keep this miserable hovel warm enough through the winter months that I don't worry about my family's health, but this has got to stop. It just has to. Keeping cool during the summer doesn't concern me much. There's shade trees to sit under, a spring to sit in, and numerous streams to lay in if it comes to that. What worries me most is the cold. Yes I realize I could mortgage the rest of my life on a home that costs hundreds of thousands of dollars that will continue to suck up electricity, propane, natural gas, etc for so long as it is standing, but I absolutely refuse. I am a staunch believer that one day humanity will look back on what we now call modern construction and say, "what were we thinking?"
Now, here's my question, and I don't know if anyone here can answer it for me or not, but you don't know if you don't try. My question is if I incorporate enough fireplaces, rocket stoves, passive solar design, and so on, is this thing going to be warm in the winter? And I'm not talking 20 degrees warmer than it is outside and we all have to stay bundled up and sit near the fireplace all day. we've pretty much got that situation now and it's pretty awful. This is also not a question of work. Some people I've read say it's a lot of work to build a rocket stove, or that incorporating a big central fireplace creates an engineering headache that's best left to the professionals. Yeah, well, nuts to that. Anything some other guy can do I can do. I just wanna know if it's going to work, assuming I incorporate enough heating sources, or is my heat just going to be sucked through the walls leaving me shivering and furious and inside?
I do plan to insulate the roof, probably with commercial grade insulation (I know I know, not a very "green" solution) and the foundation as well, but what more should I expect to do to stay nice and toasty when there's a foot of snow on the ground and the wind is howling out of the north? Should I be looking at installing a heat source (rocket stove/fireplace) in every room in the house?
And sorry if I seem kinda frustrated. I am. This is an important question for me, but I can't seem to find a straight answer. I mean, this is not Yemen, It's not even Utah or California. It gets cold here.
OK, I am going to ramble a little bit so bear with me...
I have a friend that had a large cob house, and now has a straw bale house--both in Ozark-like climate. They loved the finished product, plenty warm once the mass loaded. Monolithic mass is wonderful, don't screw it up with a bunch of cheap/free windows on the north or prevailing wind side--just a few really good windows for cross ventilation. ZERO AIR LEAKS is what you want, which cob is really good at if you don't screw it up.
They did have a huge condensation/mold problem in the springtime and much of the summer. The cool mass just collected dew and made a mess. Lots of lime to keep the wet from molding but they still had wet to deal with. When it stays cool and wet you can heat the house to dry it, but the 80 degree day/40 degree nights just turn your walls into the sides of iced tea glasses.
This time they did a roundwood timberframed strawbale. Much easier and cheaper. Mixing and moving cob is expensive--whether you are paying for diesel for a tractor or beer and pizza for your friends, it adds up fast.
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Well I'm behind you, but will warn you that if you have not done this work before, no matter how many books you read, you are going to work harder than you ever have in your life. I think that is a good thing though, and you will learn a lot in the process. Whether you build straw bail, cobb, straw clay, or a combination there in, each system has a tipping point of working and not working. I know many straw bail advocates, that claim the wonders of the system, but have done little in the way of tearing apart test walls in the more humid climates to see what is going on. I know of cobb that works fine, and others, in the same area, that sweet all summer long, there by being a health risk with mold. There are pros and cons with each system, and reaching homeostasis in you present location must be your ultimate goal. Before deciding on anyone system, look at the big picture, and what the vernacular vintage architecture of your region is. Cobb (and it's variations) is a pretty universal building methodology, thousands of years old, and if done correctly pretty bomb proof. I really need you to define some specific 1. 2. 3. type questions and I'm sure we can give you some good info as a group. We all have our individual "slant" of traditional buildings, but you can glean much from the conversation. First thing I will share is have a good design and blue print before you even think of building something. Also nonstructural cobb or straw bail, is much easier to build for the novice than will be a structural build. I am qualified to build with it (cobb) structurally, and I wouldn't, just because it is not as durable, I want my cobb for mass and thermal envelope, not working to hold it's self and the roof up.
Hi Jim, great questions and concerns. I personally think your concerns with cob in your climate is very warranted. Cob is a terrible insulation. I tend to disagree overall with the beneficial claims of the thermal mass TM.
When designing an energy efficient home in a heating climate, TM certainly can help but not nearly as much as airtightness, continuous insulation and glazing strategies. Yes you can be warm in a cob structure, possible with only one combustion appliance (RMH, wood stove, masonry heater). You will use MUCH less wood however, if you focus on airtightness and insulation uninterrupted by thermal bridges before TM. The more wood you burn, the more you pollute the exterior air, interior air and add to the risk of a catastrophic fire. I personally prefer NO combustion appliances when possible.
Air infiltration accounts for 1/3 of most home's energy use in this country. Air infiltration can also contribute to mold and mildew growth. Installing your insulation to avoid thermal bridging can also impact the energy use pie chart in a big way. Adding TM beyond what is needed in the home anyway will have very little measurable benefit in most US climates.
"If you want to save the environment, build a city worth living in." - Wendell Berry
I know very little about cob building - I have helped to build two roundwood-and-cob roundhouses - workshops not homes - and been in several more which were homes. When heated they were always toasty, that being said they are al lin the UK where it never gets as cold as it does with you.
I'm certainly not an expert on traditional building, but I am learning more as I go on, attempting to renovate and conserve my traditional stone house. This is a traditional building for my area, a house with solid stone walls approx 2 feet thick and no foundations, no insulation. Traditionally these were lime rendered externally, lime plaster internally, and heated with open fires or stoves, and were draghty. The impression many people have nowadays is that they were cold and damp to live in, because they are cold and damp now. But that's actually as a result of modern 'improvements' - including double glazing, central heating, and cement 'waterproof' render. Basically, with solid walls, they must be able to breathe. Rain hits the wall and is absorbed into the top layer of lime, and then dries out again. You create moisture inside, it absorbs into the wall, then dries out again. By covering the wall in non-breathable cement, all the moisture gets trapped inside the stone and you have wet walls, cold and damp. The modern approach is to attempt to block all draughts and make everything 'damproof' but this just makes it all worse. For these kinds of houses you must have a lot of ventilation. I'm not sure that cob functions in exactly the same way, although I suspect that it might. So it doesnt surprise me at all to hear that cob houses can suffer damp and mold - that means inadequate ventilation and/or the walls have been coated with a non-breathable surface.
You have clearly done a lot of research, but there's no substitute for the real thing - are there any cob buildings you can visit? Or any other traditional/alternative builds in your area, for comparison?
from my experimentation with cob in regards to insulation i call it fair as a insulator and fair as a heat storage medium, once the cob or mud is fired into a brick it becomes excellent as heat storage and poor as a insulator, this can be tested by putting brick on one side of a hot stove and cob (dried) on the other, the heat will penetrate the brick and not the cob
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