Building With Earth

One of the world's oldest building materials, around half of us still live or work in buildings constructed with it. Could you use it as a building material?

By Jo Smit, editor of Building4change.com

It was used to build parts of the Great Wall of China, as well as some of the world’s first ‘skyscrapers’ in the form of the traditional hundred foot tall houses of the Yemen. Earth is one of the oldest building materials and it is still estimated that around half of the world’s population lives or works in buildings constructed with it.

How Can I Use Earth As A Building Material?

There are a number of different ways of building with earth, using such techniques as cob, rammed earth and adobe. Cob involves mixing soil with straw and water and building up thick walls in layers. Rammed earth involves compacting a moist soil mix in layers inside temporary formwork - like a mould - to form walls. The same approach can also be used to build floors and foundations. Adobe is similar, but involves forming the soil mix into bricks in a mould which are not fired in a kiln, but simply dried in the sun.

Which Techniques Are Suitable For The UK?

Cob is a traditional form of building in the West Country, and large numbers of cottages have been built across the region using the technique. There are also good examples of rammed earth building in the UK, notably some experimental homes built in Amesbury in Wiltshire in the 1920s and more recently Cornwall’s Eden Project Visitor Centre. Adobe is most commonly associated with the hot climates of Spain and the Americas, but unfired clay blocks are made and used in the UK.

What Do I Need To Know?

The priority is to ensure that earth walls are protected from the most severe cold and wet of our climate, and can ‘breathe’ - absorb and release moisture. For these reasons, cob houses generally have a plinth wall of, say, stone at the base, a good overhang in the roof, and are coated in layers of limewash or a lime-based finish.

It is also important to understand the limitations of the material. Earth buildings tend to take much longer than conventional buildings to dry out – typically around six to nine months. This isn’t the building method to choose if you are in a hurry.

Earth walls also have to be very thick - generally 900 mm or more - to achieve modern, high levels of energy efficiency.

Why Is Earth Becoming Popular?

Earth is the ultimate natural material as it is plentiful in supply and generally sourced quite locally. These natural qualities have led to quite a resurgence in interest in its use in recent years.

Modern advocates are also turning to earth construction because it can be used to create curving, organic shapes and looks good. A cob cottage with a thatched roof is pretty enough for a picture postcard.

Can I Build With It Myself?

Building with earth is not as straightforward as making mud pies. It is advisable to work with a professional team to ensure that the design and construction of a home are sufficiently robust. It is possible for the non-expert to do some of the physical work, but training is required in order to get the earth mix and the build absolutely right.

For More Information

www.eartharchitecture.org Earth Architecture’s projects and publications provide inspiration and information.

www.brebookshop.com BRE Bookshop features a number of publications on building with earth, including Rammed earth design and construction guidelines and Earth masonry design and construction guidelines.

www.devonearthbuilding.com Devon Earth Building Association provides support on conservation of existing cob buildings in the area and on new build.

www.earthedworld.co.uk Earthed are artists and builders specialising in cob and other traditional techniques and educational courses.

www.cat.org.uk Centre for Alternative Technology is a key resource in environmentally-friendly building and its website includes a free information sheet on earth building.

www.clay-works.com Clay Works is a Cornwall based maker of clay blocks and restorer of cob buildings.

www.arc-architects.com Arc Architects has carried out research into earth building, some of which is available on its website.