A research process is underway to update an ancient, sustainable building material. In a successful first stage, researchers have managed to bring it in line with modern thermal standards. 

CobBauge - which combines English and French words for the material - is a collaboration between UK and French researchers, led by professor Steve Goodhew from the University of Plymouth. 

In the first stage of the project, which runs until the end of March 2019, researchers have found a way to radically increase cob’s ability to trap heat inside buildings. The technique requires use of two different grades of cob - a lightweight version with better insulating properties and a denser, stronger version - that are bonded together to form walls. 

The use of cob, which is a mixture of earth, water and fibres such as straw and hemp, can greatly reduce CO2 emissions and construction waste compared to conventional masonry materials, as it is made from soil sourced from site. However, the traditional cob that has been used in houses and other buildings throughout England and France for centuries does not comply with modern thermal building regulations. 

“While what we have come up with is without a doubt a modern interpretation of cob, we hope it will satisfy both the traditionalists and those looking for a hi-tech, energy-efficient material,” says Goodhew.

“Another aspect of the work will be in the next phase, a detailed analysis of the conditions inside cob buildings,” adds Dr. Jim Carfare, lecturer in Environmental Building at the University of Plymouth. 

“Here we’ll be studying real CobBauge buildings, subject to real environmental conditions over a prolonged period to investigate in-situ thermal performance, humidity, particulates, the presence of volatile organic compounds (VOCs) and related energy use. There is a realisation that modern building materials might have all sorts of negative consequences for inhabitants, making this work particularly timely, and creating a new focus on the use of natural materials like cob.”

“As a result of this research, we can say there is no reason why cob cannot be used to build modern houses that meet the latest standards,” says Goodhew. 

Researchers’ focus to date has been on adding natural fibres to the cob mix, however research is also being undertaken into the use of recycled by-product material such as end-of-life paper fibers. 

The next stage of CobBauge, subject to funding, will see at least two houses built using the new techniques. Researchers also hope to publish building guidelines for the new cob mixes and train builders in their use. 

Image credit: University of Plymouth