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Earthquake Testing of Cob Walls

We are excited to announce a groundbreaking collaboration with Cal Poly SLO to do earthquake testing on cob walls! Many things have fallen into place to make the project happen, including a woman who is doing her thesis on this testing, and Cal Poly’s generous offer to support this public benefit project with deeply discounted access to earthquake testing equipment and expertise ($10,000 rather then the usual $70,000!)

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Why testing cob matters more than ever:

 Conditions are all lined up for an explosion in cob building:
  • Cob is much safer for urban fire storms, structure fires and debris flows.
o   10,000 homes were lost to fire in 2017 in California. It makes less and less sense to replace these with standard construction—which is a mixture of kindling and toxic waste. 
o   Mortality from structure fires is 300 times mortality from earthquakes, and cob is inherently non-flammable, non-toxic, non-offgassing, heat-absorbing, and insulating.​

Cob is much more climate safe

Cob is much more climate safe

o   It has lower embodied energy
o   It uses less energy in use
  • Cob can be more affordable
o   Because it is so sweat equity-friendly
  • The 2017 state accessory dwelling law removed most planning obstacles to cob cottages in back yards
  • As many as 300,000 could be permitted under this new CA law
  • Precedents are reaching critical mass
o   We’ve achieved a critical mass of precedents around California, with at least three structures permitted, and two in process. 
  • Building officials and code councils are ready
o    The Straw Bale and Straw Clay appendices for the building code have gained wide acceptance. Martin Hammer, the author of these previous appendices, is working on a cob appendix to the building code (!). At the annual gathering of California County building officials there was interest in this technique, and the Santa Barbara City building official is engaged in helping permit the project mentioned below for downtown Santa Barbara.. 
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​Testing is the bottleneck

  • There is only one known in-plane cob wall test and no out-of-plane tests.Testing is needed to get basic engineering values to plug in to the equations engineers use to show that cob can take the required loads. Without these numbers, any cob permit application is basically stuck at the starting line. Numbers from cob testing can be used over and over again for many permit applications. 
*In parallel with this testing, Art Ludwig and others are working on a permit application for what could be a landmark precedent for cob building: a small village of five two-story cob cottages in downtown Santa Barbara, at an address with some of the highest forecasted earthquake forces in the state.
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