Craig, I don't know what the building looks like but I have a straw bale building, 16'x16', a small cabin. The joist system is cantilevered joist running across the sills, they run out far enough to support the straw bales. The long sills running with the plate run long to support the end joist as well. How are the original sills? Will you be replacing them? Do you have head room to place joist on top?

How is the bale wall going to be finished? Clay plaster/render?

Tim