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Cob is an ancient earth building technique which uses a combination of earth, straw, sand and water. These ingredients can be mixed together by hand, using tarps, or by machinery. The mix is formed into lumps or "cobs" which are pressed together to form the walls of a building, rather like building a giant clay pot...

Cob buildings in Broadhembury Devon, and Nelson New Zealand.

When left to dry the cob sets to become extremely hard and durable, although in wet areas like Britain cob walls need protection from driving rain which will eventually erode them. There are thousands of cob houses still inhabited in England today mainly in Devon and Cornwall. It is estimated that 30% of the world's population live in earthen homes.

A simple technique to learn, safe, non toxic and lots of fun to build with, you can use cob to create almost any structure - from the simple to the fantastic. Cob structures can be finished using different mixes of the same materials, to produce beautiful paints, plasters, floors and sculptural features.

Cob building uses the world's most abundant and sustainable building materials, has very low embodied energy, and its cost is minimal. Virtually all the materials used in the cob building process are bio degradable or can be recycled, making it one of the most environmentally friendly ways of building.

Today there are many cultures who still recognise the advantages of building with earth and draw upon the natural landscape to create their own architecture which is both practical and sustainable. Architecture which reflects the rich variety of human culture, imagination and personal identity.

New Cob buildings in New Zealand, America and England.

Cob Building Regulations and Planning Permission

Planning Permission
Planning Permission for a cob house would be sought in exactly the same way as a house using more common forms of construction. Problems that are usually encountered with planning include, where the house is built, access, design and finishes, but not specifically with the construction materials used. However building a new house out of cob can be turned to your advantage if you live in an area of Britain where the material is part of the local vernacular. This would include a large chunk of the UK, including most of the southwest into Buckinghamshire, East Anglia, Pembroke, and other more localized pockets. Planning Policy Guidance Notes (PPG’s) which might help gain approval for a new cob development over other forms of construction would be PPG12 and PPG15 which deal with Sympathetic design and preservation of the historic environment etc. Even outside these areas the governments push to promote sustainable development in guidance notes such as PPG1 could be used to your advantage if you build with cob, which is after all one of the most sustainable building materials in the world!

Building Regulations
Compliance with Building Regulations shouldn’t be a problem provided the Building Control Officer is given enough detail to make an accurate assessment. Many new cob structures have been built over the past 15 years with full Building Regulations approval such as Kevin McCabe’s new houses at Keppel Gate and the Cob Tun House, which won an RIBA award in 2005. If these types of structure are used for guidance you will not go far wrong. For a large building project to satisfy the guidelines of Approved document A which relates to structure we would recommend that the technical performance of your particular mix of cob be evaluated, particularly with reference to its density shrinkage rate particle size and compressive strength which will relate to the thickness of wall foundation and other elements of the structure. This can be done by Plymouth Universities Centre for Earthen Architecture at a reasonable cost.

The requirements of Approved Document L1, L2 that relates to conservation of fuel and power and thermal performance is probably the most contentious area for the budding cobber. This is because current regulations only measure Thermal resistance (R values), which are then translated to Thermal transmittance (U values). Using the Elemental Method to determine heat loss from a building the thermal transmittance of a wall must not exceed 0.35W/m2K. Cob’s thermal resistance is relatively poor a 900mm wall (much thicker than average) achieving a U value of only 0.45W/m2K. Therefore to comply with current regulations using 600mm thick walls it would be necessary to insulate the foundation well and use the ‘Target U Value Method’ and/or add a thin layer of insulation instead. Even better but more complicated use the ‘Carbon Index method’ which gives a more holistic view of the performance of a structure and includes type of heating including solar gain in the calculations.

However Cob proves an excellent material in which to live, it has high thermal mass and good humidity regulation. Further research into it’s properties is underway, particularly relating to the ‘Windmill effect’ which enables the temperature to remain relatively stable inside a cob structure a fact well known to the millions of people who live in cob houses across the world.
The current obsession in the building world with ‘light and tight construction’ sealing the air in a building heating it up and insulating it to stop it cooling down is fundamentally flawed. Why? Because air itself is a good insulator, and is difficult to heat up and contain without creating an unpleasant atmosphere, just a few hours in a structure of this type, an aircraft, is enough to put you off the whole concept, as you emerge shriveled, dehydrated and ill at end of a typical journey! So as far as U values go, watch this space.
Remember compliance with Approved Documents is not mandatory if other methods can be shown to work, for example it may be possible to use concrete free rubble trench foundations used by Frank Lloyd Wright and currently being used by cob builders ‘Earthed’ and straw bale pioneers ‘Amazon Nails’. Ultimately depending on the size cost and complexity of your project you will need the assistance of an experienced earth builder, and architect, or structural engineer just as you would with any other building project.

For further more detailed information see Earth Building, Methods and Materials, Repair and Conservation. 2005 by Laurence Keefe.
Or visit
www.earthedworld.co.uk
www.buildsomethingbeautiful.com
www.devonearthbuilding.com

Why build with earth?
Save - A third of the world's land mass is suitable for building with earth which means the majority of the building material can be found on or near the site. This reduces the cost of transporting and processing the bulk of materials used in construction. It also saves exploiting new resources by incorporating recycled materials into the design. Cob is load bearing and needs no framework. A house made of earth typically uses 60% less lumber than a stud frame building.

Increase - By careful consideration of the site, passive solar design and the integration of indoor and outdoor spaces, cob building increases the awareness of natural systems, our impact on them and how we can build in balance with these systems.

Reduce - Cob building reduces the need for specialist skilled labour and expensive equipment. The construction techniques we use are easy to learn and reduces the amount of money required to build structures. Typically in America a house might cost $200,000. but with these techniques people have built their own homes for less than £1000. The flexibility and fluidity of cob building allows for curvilinear shapes which enclose space most efficiently reducing the size of building required.

Improve - Cob building improves the quality of the environment, the materials used for building as well as finishes such as paints and plasters are non-toxic and non-polluting.

The importance of sustainable building

Here in the west, the industrial revolution marked a move to the use of more standardised products and materials which inevitably isolated us from our local environment, community and our own creativity. Ultimately we have been denied access to determine and shape our own buildings. Earthed provide hands on educational experiences which aim to empower people to take steps to affect positive change in their own lives and environments through creative and practical means. Building with earth is fun and encourages a sense of community. The nature of cob and the process of building is very inclusive, bringing together people of diverse backgrounds and abilities, who work as part of a team.

Building with earth encourages us to look at minimising materials and using a combination of both reclaimed and un-processed natural materials. By adapting ancient earth building techniques in synthesis with modern appropriate technology, Earthed aims to address environmental and ecological issues which affect the quality of our lives and the future of our species. Issues such as the unsustainable consumption of wood and the excessive logging that is taking place worldwide, and the pollution caused by the production processing and transport of materials.

Modern building methods are environmentally destructive and their impact on our environment is huge. The extraction, processing and transport of materials, the energy involved in their construction, maintaining the environments within them and the problems of recycling/disposal when they are destroyed creates a massive drain on our resources, pollutes our air and water and is ultimately unsustainable.

Buildings can isolate and dislocate us from the natural systems with which we are interdependent or they can empower and educate us to achieve an harmonious balanced relationship within these systems. Therefore if we as a culture wish to address with any credibility issues of waste reduction, consumption and sustainability we must develop a built environment which reflects and promotes these aims.

Sustainable building technologies, a glossary of terms

Cob - a traditional mixture of earth, sand, straw and water mixed by hand or machinery. Formed into lumps and pressed together to form the walls of a building, rather like building a giant clay pot. Cob structures are load bearing. Excellent thermal mass which is necessary for passive solar design.

Adobe - a mixture of earth, sand straw and water mixed by hand or machinery, formed into bricks which are then left to dry out in the sun. These are used in a similar way as conventional fired bricks to build walls. Adobe is load bearing.

Wattle and Daub - A woven willow or hazel framework (Wattle) is then daubed with a Daub plaster mixture of earth and dung and sometimes horse hair. Used as infill in a timber framed building.

Straw bale - Can be used as an infill to timber frame structures, straw bales are used as an very effective insulator. They can be load bearing if they are pretensioned. Bale walls are then sealed with a earthern or lime plaster.

Timber - Uses large diameter/section timber posts and beams to form a framework of a frame building. The gaps between the timbers require another building material to infill the walls.

Pise de terre - A form of cob building

Light straw - Shuttering is created to ram straw dipped in a clay slip as an infill to a timber clay frame structure. Very good insulator.

Earthships - Using discarded tyres, earth is rammed into them, they are then bermed into a bank and daubed with a cement or lime plaster.

Rammed earth - wooden shuttering is created then a mixture of earth, sand and water sometimes stabilised with cement. The mixture is rammed between the shuttering often using hydraulic machinery. The forms are removed to leave load-bearing walls, sealed with an earthern or lime plaster.