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New Cob and Earth Buildings

We have been involved in the design of over a dozen cob and earth buildings.  This Practice may have designed more earth buildings than anyone else.  The properties that we have been involved with have ranged from traditional cottage-style dwellings to those of a more contemporary and modern aesthetic.  We have also undertaken the design of new earth buildings for places such as the Eden Project.  You can see many examples of the earth buildings we have helped create in Our Projects.

As a consequence of our involvement with the repair and maintenance of existing cob buildings, we have found ourselves carrying out the structural design of new cob buildings. With our knowledge developed from dealing with existing buildings, we have a good understanding of the material and its limitations.  However, unlike existing buildings, the structural capacity of the cob has to be shown to be adequate and that this is a safe and durable building material with which to construct new dwellings and other buildings.  This will start by identifying a suitable subsoil for use in the construction of the cob walls and having these tested to determine the compressive strength.  As there is always a great deal of variation in these materials, as well as the degree of mixing, compaction etc it is always necessary to apply a large factor of safety in the same way as other materials used for wall construction such as concrete blocks and bricks.  As cob and other forms of unbaked earth are relatively weak, they are not able to support large loads unless the thickness of the wall is substantially greater than other materials.  This is part of the reason why cob walls were always much thicker than brickwork walls.  It is also necessary to avoid concentrations of load on the cob walls as it may crush under the bearing of a particularly heavily loaded beam.

So why use cob in the first place?  This material has many advantages.  Firstly, it is cheap.  It can be obtained from the site and therefore minimise the transport costs and environmental impact.  Secondly, although cob in itself is not a good insulating material, the thickness of wall and its mass has the ability to take in heat and store it when it is warm and return it when it is cool.  This thermal flywheel effect can be very good at regulating the internal temperature of a building and providing a thermally comfortable environment to live in.  Thirdly, cob is a hydroscopic material that will absorb moisture from the atmosphere when the humidity is high and return it when it is dry.  It has been found that earth buildings can regulate the internal humidity to within 5%.  This provides a much healthier environment to live in.  Fourthly, cob can be moulded and formed into irregular shapes that will provide a uniquely enthralling and aesthetical pleasing enclosing envelope.