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!!