My parents have an unfinished old 'garage' attached to their place. I'd like to insulate it and eventually finish it for them. The odd thing about the room is it's framed with vertical logs at roughly 24" on center. The outside edge of the logs has been sawed flat with 1" boards on this flat edge, but the insides are still round. The Rafters are done in the same way (cathedral ceiling). It seems structurally sound and everything is dry, none of the logs I 'poke' tested were soft. I love the way it looks inside, but they obviously can't use it as finished space in this way. I was thinking about putting foam board on the outside of the walls and roof and then re-roofing and siding over that. The inside however presents some difficulties. I'd like to keep the log look. I think it's very unique. Would it be possible to cut and trim foam board to fit in between these vertical logs and then plaster or stucco over the foam? Is it possible to plaster directly to foam board or should I use a lath product? Are there possible moisture issues sandwiching a 1" board like that?