My parents recently bought a 30 year old 2 bedroom bungalow in order to downsize for retirement. The exterior walls are sheathed with celotex fibreboard (also known as black board, buffalo board, donna conna in some places).
My father is not a fan of having just the celotex as his exterior walls (doesn't hold a nail for vinyl siding application and does not provide as much wall rigidity as other sheathing). It has gotten soft some small areas like around the bath/shower, but appears to be fine everywhere else. We were planning on resheathing with OSB, then adding 1 inch XPS, and then tyvek.
The question is can we just sheath over the celotex with the OSB or does the celotex have to be removed? Would putting the OSB over the celotex cause moisture issues?
It would seem if you put the OSB over the celotex you would just be creating a wall with higher R-value but would it cause any problems that you can think of?
Your input would be very appreciated. Thanks.