I am wanting to build a off grid home in Northeast Arkansas, considering using sand bags filled with 100% sand as wall infill of a Pole Barn building with metal roof and using a combination or wood, rock and maybe cordwood on different exterior walls. My main question is could I insulate with rigid insulation and if so would it need to go on the interior on exterior.
Do you want the temp inside to change slowly or quickly? If slowly, use "out"sulation so the thermal mass of the sand works in your favor by holding or resisting heat on the inside. If there is any clay or wood or straw in or on your walls you'll want only breathable materials cladding it, keep that in mind.
I helped build an earthbag home back in '09 at the Pine Ridge Reservation in South Dakota. It's definitely colder there than here in Arkansas. We double bagged it, an inner layer filled with our earth for the actual structure, and an outer layer of bags filled with rice hulls. Being in Arkansas, that shouldn't be too hard to find.