Cobbauge - working on the next uplift of the cob wall

A new building is nearing completion on the University campus that is unlike anything else seen in its history. Constructed from an optimised form of cob, the centuries-old material once used extensively for house building, the single-storey facility is set to become a living laboratory, a classroom and a demonstration site for a major cross-Channel research project. We talked to the researchers leading the CobBauge project to find out how subsoil and natural fibre might be the building blocks of a low carbon future.

For centuries, people built their homes from a material called cob. 

A mixture of subsoil and fibre, cob (known in France as ‘bauge’) was particularly popular in southern England and Normandy, France. However, cob does not currently comply with the thermal aspects of many building regulations across the world and has been supplanted by more energy dependent materials such as masonry and concrete. Concrete, like plastic, has become ubiquitous in its use, but it also comes with a high environmental cost. 

It’s estimated that 8% of the world’s carbon footprint (Olivier et al., 2016) is owed to concrete. 

Cob on the other hand can be viewed as an ultra-low-carbon material. It comes from the earth and can return to it once it’s served its purpose, offering one of the rationales for the CobBauge research. 
The Built Environment Department is a respected and longstanding research and teaching collective within the School of Art, Design and Architecture. It has led major national and internationally funded projects in fields such as building performance analysis, natural building materials and construction management. From using thermal imagery to visualise energy loss from buildings, to designing innovative ways for people to engage with the thermal performance of their homes, the underlying aim is to simply make buildings perform better and create awareness of the issue. 
Through this work, the department has developed relationships with a wide range of organisations in the construction sector – and this in part, culminated in 2017 with a joint application for European funding to launch a project that would examine whether it was possible to scientifically upgrade cob so that it meets today’s regulatory thermal and structural standards. 

The CobBauge project is a cross-border research project, led by the University, aiming to demonstrate that this ancient technique has a role to play in the future of the construction industry.

The CobBauge project (a merging of the English and French words for the technique) runs from July 2017 to June 2023 and has received a total budget of almost €4.1million from the Interreg VA France (Channel) England Programme, co-financed by the European Regional Development Fund (ERDF). The project partners are École Supérieure d'Ingénieurs des Travaux de la Construction de Caen (ESITC), Syndicat Mixte du Parc Naturel Régional des Marais du Cotentin et du Bessin (PnrMCB), Earth Building UK and Ireland (EBUKI), Hudson Architects and the Université de Caen-Normandie. 
Cobbauge - creating the two components of the cob building material - Invenite issue 6
Cobbauge - Monitoring the performance of the cob
The first phase of the project was conducted in laboratories on both sides of the Channel and focused on creating a cob material that was strong, yet improved the thermal efficiency of cob buildings. The CobBauge partners created four new cob mixes that were thermally and structurally tested to ensure they met building regulations and significantly improved household energy efficiency. They designed and optimised a low-density cob mix intended to maintain the material’s low carbon credentials while conforming to the thermal aspects of building regulations.
Efforts to create a material that would not exceed the 0.3W/m²K maximum U-value for walls (all insulating materials have a ‘U-value’) led researchers to develop a composite product with two separate layers for structure and insulation.
Using only natural fibre for insulation, they found they could increase the fibre volume by up to 50% and significantly drop the density and therefore improve the thermal conductivity value. This meant the structural layer could be optimised to create a density as high as required and could offer a ready-made solution for compliant low-carbon, energy-efficient, low-rise properties or the extension of existing historic buildings.
The newly created cob mixes were produced from local soils, which the project has calculated will reduce CO2 emissions by around 40% compared to the production of traditional masonry materials. They also reduced construction waste by an estimated 16 tonnes per property, a saving of €2,115 (around £1,700) in terms of landfill costs.
This image shows the distinct difference between the two layers. 
What makes this composite construction remarkable is how well the two different mixtures of cob bond together. When the two layers were destructively tested, even exerting quite large forces to ‘tear them apart’, little damage was noted. In addition, it was found that this dual layer mix complied with current thermal building regulations, both in the UK (HM Gov. Part L, 2021) and France (RT2018). The results were shared through academic papers and presentations to industry, and through public engagement, supported by the University’s Sustainable Earth Institute. The CobBauge partners work resulted in winning the prestigious EU Regiostars award for sustainability out of 50 other entries. This was clear recognition of the importance of the work.  
Cobbauge - the two sections of the cob wall side by side - strength and thermal

Having proven the concept, CobBauge moved forward to phase 2. We secured further funding from the Interreg VA France (Channel) England Programme and the ERDF for four more years of work, which would involve the construction of two full-sized buildings using the new material – one in Normandy, the other here in Plymouth. Hudson Architects, a UK practice based in Norwich with nationally leading expertise in innovative design, also joined the project team. The location for the Plymouth prototype CobBauge building is adjacent to the Sustainability Hub on campus. In January 2021, our project architect for this building, Fox Ecological Architects, submitted a planning application to Plymouth City Council. 

In being approved, the Plymouth CobBauge Building created a new landmark – the first cob building in the UK to be approved under modern regulations.

Workers on the site of the CobBauge
Cobbauge new 3

CobBauge Project - Cob houses – made from a mixing of earth and natural fibres with water.Led by Professor Steve Goodhew, a traditional building method is being repurposed through an international research project with a view to constructing a new generation of energy efficient homes.

So, how was it built? 

To produce a CobBauge building, we needed to utilise ‘formwork’ – essentially a frame into which you place the cob before tamping it down. This ensures that the walls remain ‘plumb’ straight. The structural mix goes in first to form the inner part of the building followed by the thermal layer which sits on the external part of the building, each layer being 300mm wide. The CobBauge material requires time to dry and set (through research it was found that both layers dry at the same rate, offering complementary hygrothermal properties), and the walls are built in stages, or ‘lifts’, of 500mm in height. A significant aspect of this story is about how the research can help to provide confidence for contractors, engineers, designers and ultimately the public. 
The project partners EBUKI/PnrMCB and the University are working on approximately 30 training videos, which will be shared via the website/YouTube and the project's social media sites during 2022. Working closely with PnrMCB, Hudson Architects and other partners has allowed dialogue and feedback to happen between architect and contractor right from the start about the CobBauge material. 
The completed building – a single storey, 30m2 facility – will be a demonstration site for contractors and a classroom for students, who are the industry professionals of tomorrow. There’s no reason that further innovations will not follow, and already it can be seen how it will be possible to build multiple units at once.
This building is being monitored at every stage, both for structural and thermal performance, as well as the air quality when occupied, so that the team can make informed comparisons with equivalent, conventionally constructed homes. 
The team will be putting the building through a broad range of scenarios through to the end of the project’s lifetime in 2023. In every respect, it is a living, breathing research project and has already had significant interest from the USA and Australia. There is a real sense that the construction world is watching the progress and evolution of this material. 

Through the CobBauge project, we are addressing the need for affordable, sustainable, energy efficient dwellings. 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. With authorities requiring new construction and renovations that are sympathetic to the historic built environment, there is definitely still a place for them. By developing new methods and training professionals in how to implement them, we can ensure this traditional technique is adapted so that it remains part of the streetscape for centuries to come. Of course, we understand that cob isn’t for everyone, but unless we start innovating, we’ll carry on doing the same thing and a university is a perfect place to conduct this type of real-world experiment.”

Professor Steve Goodhew