Building with StrawStraw 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• 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

Our cob bird-bench

Mixing the clay, sand and water takes muscles!

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 Cob Giant (oven and bench)

Yes, it’s the same picture, but look at the cob this time!

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!!