200+ year old colonial I am residing from the exterior. Removing everything so I am looking at the back of the horse hair plaster. Could dense pak cellulose or have open or closed cell foam sprayed in from the exterior. The problem is timing. I will be working on this a couple days at a time stripping and sheathing. I have three sides to do and I don’t want to coordinate with an installer four or five times to come out when I am ready. So my thought was to use rigid foam (its post and beam) cut roughly to size and spray foam around the edges to seal it in place. Then fill the bay this way. I was even thinking the first sheet being polyiso with foil may work fairly good because it would be up against the keys of the plaster creating a small air space for the radiant barrier to work. Like I said this is not ideal but for my situation I thought it might be a good alternative. Please punch holes in my thinking! Thanks

By the way I am installing new plywood sheathing, typar, rainscreen, and vertical grain claps. Still debating on exterior rigid foam because of detail problems it may cause at the roof on the gable ends.