On 28th March A&DS welcomed the Scottish Ecological Design Association for our third annual collaborative event on materials. This time the focus was building with earth- here’s what we learned.
1. Common as muck?
Earth Building is more common in the UK than you think. Rowland Keable of Rammed Earth Consulting confirmed that based on Energy Performance Certificate survey data there are 12,000 cob homes in England and Wales, and this only counts properties that have been up for sale. While it is less common in Scotland, earth Buildings still exist. More common in Scotland are traditional stone buildings with a clay rather than lime mortar, you can find out more about them in this HES inform Guide.
2. How High is too High?
You can build higher than you might think with rammed earth. In Central France and East Germany there are examples of rammed earth buildings up to 7 or 8 storeys.
3. Know your cob from your wattle and daub.
Earth Building rivals lead roofing for quirky sounding technical terms the most common being:
Cob: earth structural walls traditionally stabilised with a fibre such as straw or animal hair.
Wattle and daub: This is a structural timber frame with clay as an infill material.
To confuse things further these terms are not universal and Becky Little of Rebearth confirmed that in Scotland the term for cob is mudwall. The variations of which you can read more about in this Historic Environment Scotland inform Guide
Rammed Earth is a form of cob – earth mixed with clay and aggregates rammed between formwork walls that are then removed.
Clay plasters are also common as an internal finish.
4. But what about fire?
Rowland Keable of rammed earth consulting noted that earth has fireproof qualities, and has often been used in stairwells for this purpose.
5. I’m digging this, but where do you source the Earth for building?
Earth building has an enviable supply chain, Rowland Keable confirmed that up to 70% of the material required can often be sourced on site. If that’s not possible, how do you identify suitable soil? Becky Little noted that soil maps can help you identify clay soils, however the most fool proof method is to ask a farmer.
6. So as I learnt in Primary School – the wise man built his house upon the rock. So when the rain came down and the floods went up- what happened to the Earth Building?
Surprisingly – as Becky Little showed us in a slide of a Earth Building in Perthshire that stood in flooded water a few year ago – the house made of earth stood still. As a solid structure the house was able to withstand the flood water and dry out, thanks to earth’s hygroscopic (tending to absorb moisture from the air) qualities. However earth building behaves in different ways to different aquatic challenges- Becky Little also showed a slide of another building, where a pipe had been dripping against the earth wall consistently for years – resulting in a whole section of the wall washing away.
Climatic considerations and appropriate detailing are important when building with earth. In explaining a case study building- Rivergreen near Durham Rowland Keable noted that with earth it makes more sense to keep the mass (rammed earth) on the inside of the building and insulation to the outside.
In further weather considerations Becky Little noted that Adobe (unfired earth brick) is not traditional in Scotland due to issues with drying the blocks adequately.
7. So it’s thermal mass, is it thermally efficient?
Earth building performs well thermally, however Rowland Keable introduced the CoBauge project, a research collaboration between the UK and France to improve the thermal capacity of cob.
8. Environmentally, how does earth perform?
Earth Building is a low emission construction method, especially if you can source the majority of your raw materials on site – no need for transportation. In contrast cement is high in CO2.
When considering building occupants health earth buildings can be better than a lot of alternative building materials. Rowland Keable noted that the owner of a large rammed earth office block was anxious about being able to let the building after the initial tenancy came to an end. However the space was let very quickly as a result of how pleasant and comfortable it was for building users.
9. I would like to try out some Earth Building and find out more – can I?
10. Getting back down to earth – is there any technical information that can support me if I want to commission, design or build with Earth?
Yes, there’s a lot, you can find out more including guidance, training programmes and technical information on these pages here:
The Speakers at the Event were
Rowland Keable: Based in London, Director Rammed Earth Consulting CIC, Honorary Associate Professor UNESCO Chair of Earthen Architecture, on understanding current practice in Earth construction
Becky Little: Based in Fife, Becky is a craftsperson and has worked with earth since the early 90s. With a background in conservation of earth, stone and lime buildings she has wide experience of mudwalling (cob), earth mortars, wattle and daub, light earth, turf building and clay/lime finishes in both repairs and new build. Her company Rebearth specialises in these earth techniques as well as materials research, training and education. She is currently developing a range of decorative earth finishes using local natural materials.