I was thinking of doing the dual wall method. 18 inches of cob 6 inches of straw clay or hempcrete. I think the best way to do it would be to build the wall up as one, but I worry about the insulating wall getting rained on. Would it be smart to use slip forms to build the 18 inch cob walls and put ties in it, build the roof, then go back and put the forms back on the wall at 24 inches to fill in the 6 inches of insulating materials using the ties to integrate the walls together. Or, would you have a better suggestion?

Made a test brick.