Rather large 2 story home in Western WA. I currently have cedar singles for siding that are EOL and I want to replace them along with the rotting fascia board with T1-11. It turns out the sheathing is a rather thin foil faced paperboard(although it seems to be rated as structural). Some of the sheathing is also shot and must be replaced. Furthermore, it appears it no longer meets building codes due to the thinness of it.
If I were to replace the old sheathing with OSB, what benefits would I gain, if any? I have the time and money to replace the sheathing(and understand the additional complexity) - that's not a concern.