I live in a 123 year old house and I hate doing certain projects because nothing is ever simple.
I had this ugly old sheet paneling on this wall in my laundry room. The window was installed around the same time. The window isn't nice, but it doesn't have a draft or anything, so it's staying for now. The window frame actually sticks out about 3/4 of an inch from the wall. The wall has a little insulation but not much. The previous owner did this and put this foam board up then glued the sheet panels to that.
I would prefer to have the tongue and groove nailed, not only to do it correctly, but because as the wood expands and contracts I don't want it to pull away from any adhesive.
So my question is, would you replace the foam board with 3/4 plywood attached to the existing wall, then nail the tongue/groove boards to that? Or should I find 3/4" thick boards, put 3 or 4 of them vertically, then nail the new panels to those? Another option is just get longer nails and nail the boards over the foam board and into the old wall since it's made with wood strips.
As bad as that looks on the inside it would be interesting to see what it looks like on the outside.
If you want to do this right, then I'd strip that wall down to the bare studs, add fire blocking at the bottom and top of the walls, reframe that window the right way this time, install a different window, or get rid of it.
Change any wire that's needed.
Insulate, add a vapor barrier then 1/2 plywood if your going to go with T&G.
There is no need for 3/4" T&G on a wall, 1/2" or 3/8" will work.