Structurally Insulated Panels with Roundwood Timber frame

Hey there. My wife and I have been working on a roundwood timber frame all summer with a plinth stone foundation. We have 2 by 10s set every 16 inches for the floor joists and are looking at the best way to insulate. We recently came across a friend who has a connection for structurally insulated panels that are mostly used in commercial warehouses and at a very affordable price. They are basically polyiso sandwiches between two sheets of metal. We were thinking about using this for the floor on top of the joists and also for the roof. The r=values are about 8.5 per inch and go from 2 inches to 8 inches thick. Any thoughts/ reservations? Anyone have experience using this material? I know the material offgases for a year and all of these panels have been sitting for about a year. I only am thinking about using them for the floor and roof and want to do slipstraw and plaster for the walls of the house. Your information/knowledge would be much appreciated before I make the plunge! Thanks.

Why not drop them between the floor joists, even in layers with the dges sealed and then have a timber floor.
They are ideal in the roof.