Build a double wall for your exterior using the concrete blocks that builders use for commercial buildings. Fill the space with mesquite from a chipper/shredder. Seal it in. I see this as duplicating the strawbale model.
HIGHSMITH..........I`D GO WITH EITHER VERMICULITE OR PERLITE AS THEY ARE ORGANIC.THE MESQUITE MIGHT DECOMPOSE AND TURN INTO COMPOST IN THE WALL.PLUS INSECTS MIGHT HOUSE IN IT.IF YOU HAVE TO GO WITH THE MESQUITE,USE I SHOVEL OF LIME FOR EVERY 10 SHOVELS OF MESQUITE CHIPS.THIS SHOULD COUNTER MOLDS,INSECTS ETC BUT I STILL HAVE CONCERNS ABOUT THE DAMPNESS THE MESQUITE WOULD BE EXPOSED TO.
WOULDN`T A RIGID BOARD INSULATION ON THE OUTER WALL THEN COVERED WITH A FLASHING BE A BETTER IDEA?THIS WOULD HIDE THE BLOCKS AND PROTECT THEM.
CORDWOODGUY
PS:EXCUSE THE UPPERCASE AS I HAVE A VISUAL DISABILITY.