What is cob and how do we build with cob in our
sustainable homes
How we build our cob walls
Let’s
just say the way we build our cob walls is not the die hard way of cob
building. Why? Because it would normally take 1.5 years to build! (see info
below). Our clients prefer to have their homes built in 4-6 months and so do
we. Also we want our sustainable homes to get through councils easily and
quickly so that we don’t waste a year to-ing and fro-ing.
Hopefully one day earth building will allowed for in the building code, but as
of today the reality is we’d have higher costs and time frames if we didn’t do
it this way.
To build a cob wall in our
set designed homes.. this is what we do:
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Build a standard timber
frame wall as per the Building Code of Australia (BCA).
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Make allowances for your
services (put in plumbing, electrics etc).
  
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Put wires horizontally into
the sides of each section so that the clay can sit on this. Use nails on the
sides to help keep the cob in
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Mix the cob (straw /soil).
You want to be able to make a handful and be able to throw it and it still
stay together. Or so you can mould something out of it.
 
 
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To get a straight edge we
put ply or other smooth material on the back of the wall so that you can get
a nice straight wall.
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Start putting clumps of the
cob into the walls Keep going till you’re finished
  
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Try to get a smooth face so
when you render over the top of the cob, it’s easier and you use less render
  
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The lowdown and background of building with cob:
Cob
is an ancient way of building. It has been used for centuries around the world
as a building material, as well as creating art foms. The use of cob is
prehistoric in that there have been findings of its use in the 11th and
12th centuries in such areas as Maghreb (referred
by Arabs as the African countries of Morocco, Algeria, Tunisia, Libya, Mauritania Western
Sahara). Its use then spread from the 12th century to Europe, UK
and then some parts of the United States.
Cob
buildings and homes were quite prominent over a thousand years ago in the UK
towns of Devon, Cornwall, West
Country, Vale of Glamorgan, also in the Gower
Peninsula in Wales; Donegal Bay in Ulster, as well as
in Munster in South-West Ireland; and Finisterre in Brittany.
Some
of these buildings have survived over 500 years!
English
cob was traditionally made from straw, soil with clay content and water, sometimes with added sand and
gravel, and put onto stone foundations in numerous courses. The walls were
thick, up to twenty four inches thick and provided large thermal mass in the
walls. Lintels for doorways would be made and openings for windows would then
be allowed for. In most instances it would take nearly 1.5 years to build a cob
house as you can only build a new course after it has fully dried and shrunk.
You can only build a course up a certain height otherwise it will slump.
Building with cob today and it’s revival:
You
wouldn’t believe it today because it seems we’ve been building with cob for
many years now, but in 1994 Kevin McCabe built a cob house in England in 1994
which was supposedly the first cob house built in the country for over 70 years.
He added sand and shillet (crushed shale gravel) to reduce the shrinkage of the
clay. The revival of cob has only really been around since early 2000 so although
it’s relatively new compared to modern building techniques, it’s actually an
old age building material and method.
It
is estimated that 40% of the world’s population live in earthern dwellings.
Sooo.
It’s great that there is a resurgence of interest in natural, earthern homes
and buildings.
Pros
It
makes sense afterall. It’s clean, energy efficient in that it’s solar passive
(allows the building to be warm in winter and cool in summer), keeps humidity
out of the air (great for winter and keeping the damp away from our bodies,
clay also removes impurities from the air.
It’s
natural and in your back yard or can be sourced easily. Is cost efficient, you
don’t need to be skilled to build with it.
Clay
and natural materials are better environmentally for numerous reasons. There is
less electromagnetic radiation than say steel or metal. Conventional bricks
require high amounts of energy to make, they are also rigid, being cement based
and are therefore brittle.
Cons
For
building commercially it takes a long time to build a cob house or wall because
you can only make 300mm course in one go. Then you have to wait 1-2 months for
it to dry and shrink fully then go again. So if you’re owner building and
building your own home, time you have.
It’s
also not in the building code so the traditional way of building cob walls have
to be engineered (if an engineer will approve a 24 inch cob wall) and council
will have to approve it. The irony is that cob homes seem to withstand
earthquakes better than conventional homes but that’s another story.
Or
if you’re like us we will be structural framed walls and then infill with cob.
It’s not the true cob wall but it makes it more practical to build and makes it
easier to get through councils.
References:
http://en.wikipedia.org/wiki/Cob_%28material%29
http://www.buildsomethingbeautiful.com/
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