DCRS Article
Building with earth – isn’t that old fashioned?
By Rob Buckley of Dorset Centre of Rural Skills
Building with earth could be described as old fashioned as it is our most ancient form
of building and started with mud huts. Earth was also used in the construction of
some of the worlds greatest architecture and today it is still used to build beautiful
and individually sculpted homes.
One method of earth building is known as cob. Traditionally the mixing was done in
a pit with animals to trample and mix the earth and straw. This inevitably meant the
addition of waste matter in the mix, and lead to a common belief that cob would only
work if a small percentage of dung was used. This isn’t true at all and no dung is
required! These days cob can be mixed by rotavator, or if on a large scale, with a
JCB. Cob is actually a mix of subsoil, either clay or chalk mixed with straw, and is
relatively wet to build with. Walls are formed by either pressing and sculpting the
cob, or shuttering can be used.
Curved walls are easy to build as well as features
and designs can be carved into the walls.
Another popular method of building is rammed earth, the original French term being
Pisé. The technique came from the Romans and was taken up in the eighteenth
century in England. Rammed earth differs from cob in that you just use damp
subsoil, again either clay or chalk.
The earth is literally rammed with shuttering
under a lot of pressure to form walls. The advantage of this method is that that the
process is quicker and the building won’t shrink so much when drying.
Dorset Centre for Rural Skills, West Farm Barn, Farrington, Blandford, Dorset, DT11 8RA
Historically, earth building has been very popular in the South West, from the chalk
hills of Dorset through to the clay sub-soils of Devon, and there is plenty of evidence
of this around us in the pretty cob cottages in most villages throughout the
Blackmore Vale. The disadvantage of cob building is that it is relatively slow and
labour intensive, and so it was superseded by bricks and blocks. But, in light of the
need to reduce the CO2 released during the construction of buildings, known as the
‘carbon footprint’, earth building has become viable.
Chalk sub-soil and straw are readily available in this area, often on or near the site
almost eliminating the need for transport making this a highly sustainable building
method with very little embodied energy. Earth is an abundant, recyclable, non-toxic
material and benefits from having a high thermal mass, or in other words, the
building stores heat.
Most people are familiar with the concept that many older
houses are cool in the summer and warm in the winter, and these will most likely be
cob or mass stone.
This thermal mass can be used to greater effect with the
benefits of solar gain in the design and orientation of the building. By making the
most of winter sun, the need for heating can be reduced. Unfortunately, it is difficult
to make an earth building meet current building regulations on insulation, and they
usually require extra external insulation to meet requirements.
But the complex
effects of thermal mass are being researched and are showing benefits greater than
insulation on its own.
Earth buildings can last hundreds of years if properly maintained. The walls are load
bearing and structurally sound.
This has been assumed for years, but now with
modern technology structural engineers have proved that this is true.
Sound
Dorset Centre for Rural Skills, West Farm Barn, Farrington, Blandford, Dorset, DT11 8RA
proofing is better than an average brick build, and lime rendered earth buildings,
unlike modern brick buildings, are breathable.
The environmental benefits of earth building are so great that it has to be considered
as an alternative building method to cut down current carbon emissions and energy
use in the construction industry. Earth buildings have low carbon footprints and the
materials are locally sourced. Now we have the technology to take advantage of
earth building and can use modern manufacturing methods, such as the ability to
make cob blocks.
This leads to a natural transfer of skills where most of the
workforce in the building and construction industry are already trained to build with
blocks. The answer to creating a low carbon producing construction industry isn’t
easy, but with the help of modern technology applied to cob and rammed earth
building techniques, we are equipped to make a significant environmental change
and at the same time, build beautiful, individual houses.
By Rob Buckley
DCRS
Dorset Centre for Rural Skills
Notes:

This article cannot be used or published without permission from
DCRS.

This article must be attributed to Rob Buckley of DCRS
Words:
734
Dorset Centre for Rural Skills, West Farm Barn, Farrington, Blandford, Dorset, DT11 8RA
Issue Date: June 2006
Contact:
Nicky Mullen, DCRS, West Farm Barn, Farrington, Blandford,
Dorset, DT11 8RA
Tel:
01747 811099
Email:
info@dorsetruralskills.co.uk
Dorset Centre for Rural Skills, West Farm Barn, Farrington, Blandford, Dorset, DT11 8RA