What I thought was really interesting and rewarding about the natural building week was the chance to listen to Micah talk about 'natural' enclosures for timber frame structures. Straw bales are of course an option and have their own issues. There is also the Structural Insulated Panel option, or some combination of conventionally framed walls (though that may seem a bit redundant). What Micah proposed was a light framework stuffed with a compacted straw clay mixture. You mix the straw (we did it with a pitchfork on a big table but you could set up a rotating drum mixer) with clay slip-a watery clay mix, and then pack the stuff down into formwork built between the timberframe structure. Once the straw sets (quite quickly) you remove the plywood forms and work your way up the wall; this is nice because you can repeatedly re-use a single set of forms. In this example structure, he also showed how you could make the walls with lathe to later accept natural clay plaster.
Corner detail with minimal thermal bridging.
Mixing the straw and clay slip.
Tamping down the corners.
It was amazing how quickly the wall setup, and even more so how solid it was after only a few hours. Breaking it down the next day was like busting up concrete.