Improving Cob's insulating ability

cob research
“The issue is getting through building regulations, specifically Part L,” explains Steve Goodhew, the Plymouth University professor leading the project.
According to Goodhew, a cob wall would need to be over a metre thick to meet the minimum U-values stipulated in Part L. “Anyone with a commercial sense isn’t going to accept that,” he says.
The project aims to make cob a commercially viable proposition by backing it with clear performance and usage data, ensuring that wall thicknesses can be kept below 600mm and built easily with industry standard equipment.
One way of boosting the thermal properties of cob is to incorporate a higher percentage of straw or other insulating material.
The downside is that the greater the percentage of insulation used, the weaker the mix.
“There is a relationship between density and strength,” explains Goodhew. “We found that we can’t get a cob mix that meets Part L and Part A [structures].”

This is to do with insulation and load bearing factors.

Thank you for posting that, I have just been looking at cob building and wondering if it would be able to pass the new insulation requirements.
Now I just need to find more info on cob as a retaining wall and my pie-in-the-sky idea might be able to get somewhere...

I enjoyed reading this article and seeing the industrial approach to using cob. Thanks for posting this John.
That said, I look back fondly on years of using wine, champagne, and beer bottles when building with cob for improving insulating ability. Bottles forming a thermal break (insulating effect) have been fantastic for wood fired ovens using clay/sand and cob. Vertical walls hold up very well with cob surrounding sturdy bottles. I have used them in building outdoor walls for their beauty with the sunlight and to reduce the quantity of cob one must mix. These applications have held up like new over the last 20+ years. For the small scale builder who is looking for insulating ability, and a reduction in time/labor mixing large quantities of cob, bottles seem to be such a natural fit for providing thermal breaks, reducing labor, and supporting recycling efforts. In addition, humans have a need for celebration so sourcing bottles for building through celebratory events satisfies both the need for shelter, community, celebration and the need for connection. Maybe bottles vary too much in individual glass wall thickness to be codified for regulating professional builders. But if a person has the freedom to create, use well reasoned judgement, and explore possibilities, bottles have a lot to offer for insulation and more.

Wow, thanks for that article on cob.

Pippa, unstabilized earth such as cob is not a good choice for a retaining wall or any place where it will be in direct contact with the earth. For a retaining wall, you need a material that won't soften when it gets damp.

Thank you Rebecca. I did a bit more research after that and came to that conclusion too.
Will have to be done kind of hybrid then, with an air gap behind the cob wall then, I think.

I have heard of people making an insulation sandwich when building with stone, could you do the same with cob? Cob on the outside, insulation, and then cob on the inside?

I wonder,  would charcoal improve the U value of cob, without weakening it?