Shantytown notes: "I asked about earth plaster over rigid foam. and people were like eww rigid foam off gas off gas.... why not just do a very light straw clay infill or just pack in straw... but if you have to what you would do is tack up some newspaper and put up lath and then plaster over the lath." Main reason for not using straw: desire for insulation AND need for light weight AND with 7'6" wide dimensions, encroaching on interior space is also an issue---otherwise I'd do 12" thick straw/mud walls. What I'm currently planning is using the free-found rigid foam, putting some kind of initial rough layer directly on top of the rigid, and a thin coat of plaster directly over that. HOW DOES THAT SOUND?