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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
A cordwood wall is another natural building method using stacked “cordwood” (debarked tree pieces) and mortared with cob or masonry mixes.
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.
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, 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.