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New meets old: Cob houses enter the twenty-first century

Photo: CobBauge Project

A marriage of new and old wall materials using earth and plant fibre has won the first prize in the category “Connecting Green, Blue and Grey” at the European Commission’s RegioStars Awards in Brussels, as part of the European Week of Regions and Cities.

Cob houses are made of compressed mud and straw and have traditionally been built in the south of England and Wales and northern France for hundreds of years.

Some houses exist that are older than five hundred years. These earth-based houses are also found in rural landscapes in many other parts of the world.

They are breathable, they store carbon and solar heat in their structure, and they are comfortable. The modern versions will also be cheaper to heat and cool, and at the end of their life can be easily recycled and therefore contribute to a more circular economy.

However, it’s hard to get these buildings through the modern regulatory system because it’s not easy to prove that a field-made cob material meets both thermal and structural requirements.

Satisfying these requirements was the objective of the CobBauge project. A partnership of Norfolk Council, the University of Plymouth, England, and earth-building charities, it is part of the European Union’s strategy to reduce carbon emissions by 20 per cent by 2020.

The CobBauge project has tested four new cob mixes thermally and structurally to ensure they meet building regulations and significantly improve building energy efficiency.

Traditional technique

Traditionally, the material is very labour intensive, involving the careful selection of the right kind and consistency of mud, mixing it with straw, and compressing it manually into the wall form. The result is often organic, freeform and deliberately uneven, giving a building a warm, hand-made feel.

CobBauge has evolved this technique into a labour-and time-saving manufacturing process that results in a product that’s much easier to use on site.

A modern hand-made cob house– the clay mix can be sculpted into beautiful shapes

This material can reduce the CO2 emissions of production by around 38 per cent compared to the production of traditional masonry materials, and reduce construction waste by an average of 16 tonnes per property – also a saving of 2115 euros (AU$3440) in landfill costs.

The prize it’s won is an annual one awarded by the European Commission to projects funded by the European Union that have demonstrated their excellence, and the value of their innovative approaches to regional development.

Demonstration buildings and jobs

The organisation is planning demonstration buildings and has drawn up a directory of building professionals interested in using the modernised cob, who will be offered training in construction methods.

The proof-of-concept buildings will be occupied and monitored for energy use, thermal conditions and indoor air quality, for comparison with equivalent, conventional homes, and piloted by Hudson Architects, a UK practice, and Francois Streiff at PnrMCB in France.

“We believe cob has clear advantages over other materials in terms of the energy needed to construct it and bring it to site, and the construction of these homes will also make use of the traditional skills of small businesses and tradesmen in areas where cob has historically been used,” Professor Steve Goodhew of Plymouth University says.

Building guidelines will be published, and once the system is finalised it is intended to provide 1500 affordable low-carbon 

The new cob material in development for mass production

modernised cob buildings over the next ten years, jobs in sustainable housebuilding in rural, often low-income areas, and preserve the cultural heritage of an ancient building tradition.

The organisation tested 20 different mixtures of earth and plant fibres and chose the two best-performing mixtures from France and the United Kingdom to ensure local production, then optimised the distribution of mud and fibres in walls to enhance the insulation, stability and indoor air quality.

Specially designed frames support the wall pieces while they dry, which helps them to lose moisture more quickly during production.

“These architectural traditions and skill-sets will be lost if concrete and plastic become ubiquitous The CobBauge material gives a high-performance, low emission, low-embodied-energy future to a traditional building form, preserving and enriching regional cultural identities,” says Karen Hood-Cree, project manager, University of Plymouth.

The researchers estimate that these houses will save EUR 11 million (AU$18 million) in construction, energy and materials costs compared with 1500 traditional houses over their lifetime, and will eventually be cheaper than similar passive houses.

David Thorpe is the author of Passive Solar Architecture Pocket Reference, Energy Management in Buildings and Sustainable Home Refurbishment.

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