Building with natural materials


natural building materials. J


One of the ancient methods of construction that can be found throughout the world uses just clay rich earth, straw and water. Although we don’t automatically think of these materials for modern house building, they are still used in traditional cob building, and the time might be right to see their return to main stream construction.


There is a long tradition of building cob houses in the South West of England and in parts of the North West, some of which are over 500 years old and when resold can fetch unbelievably high sale prices. So what makes a cob house so desirable? Apart from their obvious uniqueness and aesthetic appeal, we need to understand the advantages of using natural materials in this method of construction and the benefits they offer for a healthy living environment.


Firstly, clay rich earth and straw are not only used for the structure of the building they are also used effectively in plasters, mortars and earth floors. They are simple breathable materials; 100% natural and highly sustainable. Importantly, the use of cob has shown to provide passive environmental control in


66 Listed Heritage Magazine September/October 2018


buildings through the buffering of temperature and relative humidity.


To explain briefly, as your house heats up through the heating system or solar gain, the cob heats up and thermal energy is stored in the walls, not just the air. When heat starts to flow out of the building, the stored heat starts to discharge into the room passively warming the space. This creates a more even internal temperature between day and night and reduces the load on your heating system, decreasing fuel bills.


The same role is performed with humidity. During times of high humidity, clay rich earth will absorb the excess moisture from the air. During times of low humidity it will release the


Constructed clay earth wall


im Matthews, a partner at HG Matthews Ltd takes a look at traditional cob building and explains the advantages of using


Harvesting straw for block making


stored moisture back to the air. This keeps the internal humidity within the optimum range of 40 - 60% for a healthy and comfortable environment, decreasing the risk of respiratory infections, inhibiting mould formation and preventing condensation.


NATURAL AND EFFECTIVE Traditional cob houses are made with a varying mixture of clay rich earth and straw, depending on the soil type in the build area and by adding water. The wet cob is shaped by hand and applied in thick layers. Once dried, the layers are trimmed to shape and protected with external and internal breathable wall finishes. The construction process is labour intensive and weather dependant. But the advantages far outweigh


Continued >>


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