This is the eighth post in our Super Natural Materials series - you can view the whole series here.
What is cob?
Cob is a mixture of sandy-sub soil, clay and straw. It's mixed by crushing the particles together by either dancing on it or using the head of a digger. The sandy-sub soil must be sharp and ideally contain angular stones and gravel - this will make it stronger. About 75% of cob is made up of this sandy aggregate. Any type of clay can be used, but be careful not to use silt which can sometimes appear like clay.
It's a strong and durable material - houses can last for a very, very long time - if maintained and looked after properly. The oldest standing cob house is reportedly 10,000 years old.
In places where timber was scarce, the building material most available was often the soil underfoot - local and natural materials were and still are, the cheapest and one of the most sustainable ways to build. Cob construction is easy and doesn't require any fancy equipment or specific training. Its thermal performance varies by climate region - while cob is a relatively poor insulator, it also has the ability to absorb larger quantities of heat.
Benefits of building with cob:
- Sustainable - the most sustainable form of building there is - cob has almost zero embodied energy. Since its made of earth, it his also entirely recyclable and non-polluting.
- Affordable - as long as you have land to build on, anyone can afford to build cob walls.
- Breathable - its a healthy place to live, as there is no damp in a cob house.
- Requires almost no heating - if you design your cob house on passive solar principles, you can get around its poor insulation properties. To do this, you should use cob on south facing walls, making the most of its thermal mass. Then, us e straw bales on the north facing walls to provide great insulation.
- Aesthetics - with cob, you can practically sculpt it, meaning that you can create curves and even carve shelves into the walls.
- No chemicals or additives
- Sustainable load bearing
- Long life spain
- Doesn't burn
- Insects will not eat cob
Examples of building with cob:
Cob Cottage: "A cob cottage in the West Country, where the soil has the ideal proportion of clay required for this method of construction; A cob inglenook, with an attractive uneven finish, houses a wood-burning stove." via Period Living.
Keppel Gate: "Keppel Gate is situated at the end of a long no-through lane, just outside the East Devon town of Ottery St Mary, which is one of the oldest and most historic small towns in Devon." via BuildSomethingBeautiful.
Hobbit Hole: "A farmer built this cottage for just £150, using only natural or reclaimed materials, and is now rented out for a fee of fresh milk and cream. And with no mains electricity, gas or water, the bills don’t come to much either." via BBC.
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