Arched soil roof? Earthen plaster?
First off I need to State I am a huge fan of what you're doing!!!! Awesome & inspiring!!!! Have you considered not using wood or sealing your Wall Systems?
These structures will last 1000 years or more without wood. Using Earthen plasters inside and out will allow the structure to provide evaporative cooling inside on hot days as well as provide warmth and slight humidity on dry cold days.
You guys give me hope for this world!!!
Is this a good question?