Where is the vapor barrier in a clay/straw wall?
No vapor barrier is necessary in a 12″ thick clay/straw wall. Clay has the ability to hold many times its weight in moisture without deteriorating. It has the ability to wick water away from wood and straw and to release the moisture back into the air when the ambient air humidity drops. The clay itself acts as a huge network to intercept, hold and then release moisture in the first couple of inches of the wall so that no significant amount of moisture ever penetrates to dew point. Therefore a vapor barrier is not required and in fact would be detrimental to the wall because it would trap moisture setting up conditions for decay.
