Building with Straw
Straw bale, Cob, and Light Clay Construction
Alison Ray
20 September 2004
An experience with straw: Bioconstruindo 2004
Heidi: Queen of the Strawbale Pile
Brazilian Cerrado, Rippin’ the Curl
Bioconstruindo: bamboo geodesic dome, vigas reciprocas & ferrocement caixa de agua
Quick History of Straw Bale Homes
• 1800s – Nebraska: Settlers
• Lumber expensive and sod
too precious but straw was
extremely abundant!
• Invention of horse-powered
baler in mid-1800s and later
steam-powered made home
construction faster and more
efficient
• Warm in winter and cool in
summer, not just a
temporary thing
Constructing a Straw Bale Space
• Straw bales are stacked
like blocks to form the
walls of a structure
• Load-bearing walls
• Infill for post and beam
• Straw bale walls are
highly insulative (up to
R40), sound proof, and
when plastered resistant
to fire, vermin, and
decay
• Works great in
combination with cob
Laying and sewing the bales
Binding the bales with wet cob
Nearing the top
Natural plastering: cob and clay
Almost done
Quick History of Cob
• Cob is an old Devon word for ‘mud wall’
• Cob has been Devon’s traditional construction material since 14th century.
• Traditionally, straw and dung, were added to the clay sub-soil to reduce
cracking
• Cob can last for many years so long as it does not
accumulate moisture
• Some houses in England are 600 years old and still standing
Cob Construction
Our
cob
birdbench
Mixing
the clay,
sand and
water
takes
muscles!
• Cob is a mixture of
clay and sand (earth),
straw, and water
• Cob walls have no
structural elements
• Natural plaster or
rendering must be
applied to prevent
moisture
• Cob is favored for its
freeform quality
Advantages of Cob
• Abundant, inexpensive and
replenishable material
• Free-form, creative and artistic
• Easy to do (and fun!)
• Structurally more stable than
conventional homes to earth
quake
• Cob is a flexible material that
moves with the Earth’s
movements while staying
together (allowing for rounded,
natural shapes
• Provides thermal mass, storing
sun’s energy and releasing it at
night but also cool and shaded
in the day
Cob socials! Fun to dance and play with the earth while creating functional art!
Inserting a window into a cob wall
Forming
cob bricks
from the
wet
material
Cob wall with tree stump decoration
Yes, it’s
the same
picture,
but look
at the
cob this
time!
Cob Giant (oven and bench)
Taipa Leve: Light Clay
• German tradition for over
400 years
• “Leichtlehm” or “Wattle
and Daub”
• Timber provides most of
the load-bearing structure
• straw, earth, woodchips,
sawdust or any material
provide insulation and infill
• Panels created to be
independent so houses
could be easily
deconstructed and
transported
Using Light Clay Construction
• Loose straw or other material is coated in a clay slip then
tamped into temporary forms for infill of a wood frame
• The material will dry about 1” per week, an applied
plaster prevents moisture from entering the wall
• Panels are light weight, insulative, non load bearing and
great sound proofing
• This technique can also make sawable construction blocks
Creating light clay walls
Tamping down the walls
Building the Walls
Natural Building is good for the environment, for human health,
and community-building, but most of all…
it’s fun!!