Cob is a mixture of clay, sand, straw, and water. To build a cob house you will essentially need three main components: foundation, walls, and a roof.
Here are some of the different styles and systems for building a cob or a hybrid cob home. A hybrid cob home is basically any home that is partially constructed out of cob and partially constructed out of another material.
Depending on your climate or design you may want to incorporate different materials into your cob house to take advantage of different attributes or styles.
Foundations
Rubble Trench
For proper drainage, it’s important to build a rubble trench below the perimeter of your cob building. It’s located beneath the stemwall and is filled with drain rock (small stones or round gravel).
Once the trench is dug, it is good to cover the bottom with a few inches of drain rock and then lay a 4-inch perforated polyethylene drainpipe along the bottom to improve the drainage runoff. The bottom of the trench should also be sloped.
Stemwall
Stone
You can use any type of stone that you like. Stones give the house a natural and homey charm to a cob house. However, the stemwall may be one of the most expensive parts of building a cob home due to the cost of stones.
Urbanite
If you want to save money constructing your stemwall then you may want to consider using urbanite instead of stone. Urbanite is recycled concrete that comes from old sidewalks, buildings, etc. It is very versatile, free, and lasts practically forever.
Fired Bricks
Another option is to use fired bricks. They can be any type. The price can vary, but you may be able to find old ones to save on money.
Concrete Blocks
You can use solid concrete blocks or cinder blocks. Cinder blocks work, but I would not recommend them due to their fragile sides. That’s just my personal preference though.
Poured Concrete
You can also create forms and pour concrete for your stemwall. This just seems like a lot of extra work to me though. Creating forms and filling them all with cement. It is more technical and doesn’t look as nice or natural as stones.
Wall Systems
Adobe
Adobe is very similar to cob except that adobe is shaped into bricks (with forms) and dried in the sun. Then the dried bricks are stacked and mortared together.
Bale Cob
If you live in a region that gets very cold in the winters, you might want to build a hybrid bale cob wall system. A bale cob wall consists of stacked strawbales covered with cob on the sides and mortared together. This provides better insulation value. Even if your winters don’t get extremely cold, you might consider doing bale cob on the West and North walls of your structure. These are the sides that get the least amount of sunlight.
Cob
If you are reading this article, then you are probably already thinking about building your home out of cob.
Cob is an excellent building material to use for your home. Read more about the characteristics and advantages of cob.
Cordwood
A cordwood wall is another natural building method using stacked “cordwood” (debarked tree pieces) and mortared with cob or masonry mixes.
Earth-Sheltered
You can make earth sheltering walls to increase thermal mass and better insulate your home. Earth sheltering is an ancient method for building and insulating homes.
Straw Bale
A straw bale wall is constructed entirely out of straw bales and is covered and protected in layers of plaster. Straw bale walls provide excellent insulation value and are quick to construct.
Timber Framing
Timber framing, also called “post and beam” construction, is a building technique using carefully fitted and joined timbers with joints which are secured with large wooden pegs. The inside framework can be filled with cob, wattle and daub, or similar materials. This method is commonly seen in the traditional German Fachwerk homes.
Wattle and Daub
This is a technique for building walls in which wooden strips are woven together into a lattice. Then it is “daubed” with a sticky soil material that usually consists of earth, sand, dung, and straw.
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I’ll start my home this spring if everthing goes right . been wanting to Build a strawbale or cob home for years now. just bought a piece of land and make it my Home
Congratulations and good for you. I hope the same for myself this year. Where are you building? Would love to be of assistance.
Does anyone know if there are restrictions on where cob homes can be built. I am planning to get myself some land and start my own humble abode. Some information on this will be very much appreciated.
Oh and congrats Ron, I hope you have a great time with your build!
Hi Amos,
It’s going to depend on your state and local county building codes. Research the building codes for your particular state to find out how lenient they are with cob or alternative buildings. I have an article on this topic here: http://www.thiscobhouse.com/cob-building-codes-and-cob-permit-requirements/
I also wrote a document called “Cob to Code” all about building codes and permits as they relate to cob homes. It’s available here on the site for $20. http://www.thiscobhouse.com/cob-building-codes/
Anyone else from Oklahoma and considering a Cob home? I’m concerned about cracking during our intensly hot summers.
We are looking at property now. In the mountains of Virginia/ west Virginia. Also we are looking at buying a piece in Northern Minn. Of the different cob houses which would be better for the cold. Plain cob or a hybrid of straw and cob?
A hybrid of cob and straw bales would be the best for a cold climate if you still wanted to use cob. You might consider using straw bales on the north and west walls of your house and cob on the south and east walls depending on the shape you design it.
Awesome! I will incorporate this information into my designs. Thank you.
have started to build my oven.building the plinth cleared my garden of a good ton of old brick and rubble.(thats a saving of €240)no need to hire a skip.
I have found a source for clay by a river at the back of my house,again it’s free. the sand and straw i can access for free.
while i am completing the oven i am starting on the foundations for my cob house.by pure luck i have a source for timber again for free.my main aim is not only to build with out spending money on it.(with the exeption of transporting goods needed etc.) and also try not to get carried away with myself on the structure.(very easy to do). i would like to try and incorporate a small oven that i could use to heat the rest of the house.i havent even worked out the square footage or planned the room space.all i know is i am going to build this home for less than the price of a weeks shopping!! any help comments ideas are most welcolme.
Is that tru about urbanite? (not that im implying your wrong) its just that i have read from time to time about how peoplpe see theres crumble… was just wandering if this is more to it being built poorly. thanks