Building Your Own Cob House

More than one third of people in the world today live in homes made of earth and we’re not just talking about third world countries. Records show that cob houses were being built in England as long ago as the thirteenth century. Very old cob houses built without the use of bricks or wooden supports are still being lived in in many parts of England and Wales, but especially in the West Country.

Cob consists of mud and straw, and it’s one of the oldest forms of building material in the world. Though it was a popular choice for mediaeval farm labourers it wasn’t just the impoverished who lived in cob houses: examples of cob manor houses are still standing today including one at Hayes Barton, which was the birthplace and much-loved childhood home of Sir Walter Raleigh.

Although cob building went out of favour in the late nineteenth and early twentieth centuries its attractions are again being recognised. In the 1980s a new generation of cob building enthusiasts came to prominence and in 2009 an architect-designed cob house, described as eco-luxury, sold for three-quarters of a million pounds.

The Advantages of a Cob House

  • Because the walls are necessarily thick they provide good insulation and they also retain heat well. A cob house will typically use 20% less energy to heat than an equivalent modern house.
  • The mud walls absorb humidity from the atmosphere and release it when the air dries out resulting in a healthier living environment.
  • Using local subsoil means the house will fit in aesthetically with its surroundings as well as being sustainable and eco-friendly.
  • Building costs are cheaper especially if you do it yourself.
  • A cob house doesn’t need a wooden framework thus saving trees.
  • Building with mud allows for a more creative approach with curves and other architectural features being more easily shaped.

The Disadvantages of Cob

  • Building takes a long time and each stage can only be completed when it’s dry and warm for a reasonable period of time. (See How a cob house is built)
  • It’s hard manual labour.
  • And less seriously, to allow them to breathe the walls have to be kept clear. As one cob-home-owner said, ‘It means we can’t grow roses around the door.’

How a Cob House is Built

The foundations for a cob building are made of stone to prevent rising damp; it’s the walls that are constructed of cob.

Subsoil, straw and water are the essential ingredients. Depending on the geology of the area the subsoil may be more or less suited for cob as it must contain a good proportion of clay. Aggregate is usually added to increase the resistance of the cob to poor weather conditions.

The ingredients are mixed together by hand, with mechanical tools or by getting cattle to trample it. The straw keeps the block together while it’s still wet and when it’s beginning to dry it can be shaped as required.

Blocks are usually made to be about 2’ high and thick. After positioning, a layer (or lift as it’s called) has to be left to dry to allow for shrinkage in height. A week of good weather is needed for this process after which the lift is compacted and strong enough for the next lift to be added. It can take 3 months for a typical 2-storey building to reach roof height, and even then the roof can’t be added immediately. Nor can the windows and doors as it’s necessary to wait for about 6 months for the walls to finish shrinking.

So building a cob house is a not fast process: it can take 15 – 18 months depending on the weather. It can also result in losing friends if you ask for help too many times!

Ideally cob house building is a communal project involving a number of people all with the same dream of building their own eco-friendly sustainable homes, co-operating and sharing muscle-power, abilities, inspiration, and the ups and downs – much as it was done in the past when farm labourers would work together to complete a cottage in a season.