Print This Page

Cob

Defined
A cob house is made of clay, sand and straw. The mixture is "kneaded" like dough before it is put into place by stomping on it with your feet or using a cement mixer for larger scale operations. The clay acts as the glue, while the sand gives strength to the mixture and the straw gives the walls tensile strength once hardened into place. Because cob is very flexible to work with, the builder is free to create just about any shape, so you won't find too many cob homes that look similar to each other.

History
Cob is a very old building method that is now enjoying a renaissance. There are homes still standing today in Wales that are at least 500 years old. Chances are these homes were built out of earth out of necessity rather than choice. They were probably built by rural families that were extremely poor at the time.

 

 

What are the advantages of building with cob?

  1. Energy Efficiency - A cob house provides a large amount of thermal mass. This helps keep the house cool in the summer and warm in the winter. I'm not certain if anyone has tried to build a double-wall cob house, but for cold climates, some sort of cob-insulation-cob wall might be more appropriate.

  2. Inexpensive - The walls of the home are made entirely of natural resources that are available under your feet. This brings up a good point about natural building in general; use the natural materials that are prevalent in your area. Clay is abundant in most areas of the world. Why not build with what you've got?

  3. "Buildability" - Cob homes are owner built. There is obviously, quite a bit of labor involved but if time is not a factor, a house of this type could be built with just a couple of workers. Basic carpentry, plumbing and electric skills are required.

  4. Fun - If you like playing in the mud, this is the house for you. Seriously, this is an excellent style of house to build for those with imagination. You can be very creative with the walls of your house.

What are the disadvantages of building a cob house?

  1. Resellability - With any other alternative house building types, you might have a problem reselling a house that is "different" from the norm. In most cases, the occupants who build alternative homes are usually building them for a lifetime, but if plans change and you need to sell, it may take longer to find a buyer.

  2. Building Permits - As with all alternative building methods, you might run into some problems with local building codes. The walls are the biggest hurdle. The rest of the house is built using conventional building methods, but getting approval for the mud walls might be a problem.

  3. Financing - Cob homes are quite unique to say the least. Uniqueness is not a word that lending institutions like to hear. But why would you want to finance a cob house in the first place? It's probably the least costly house you could build and the cash outlay is minimal.

  4. Durability (It depends) - Cob does need to be protected from the elements. A large roof overhang will protect the walls from all but driving rains, but weather will take a toll on the walls. Reviewing the houses that were built in Britain over 500 years ago, I noticed that these homes were finished with a stucco type material. Depending upon your climate, you may need to consider some type of finish to protect the cob.