Installing fiber cement siding over existing cedar siding
Is there any building (tar) paper? We always installed paper over celotex in the early '70's when I started framing.
Is the bevel failing everywhere, or just the weather side?
A picture would be helpful. And may I ask, where is your location?
If you are set on replacing the siding, I would remove the cedar. The black board - celotex, is keeping the walls from racking. I would use 30# tar paper or Typar, much better than Tyvek, in my opinion. The new siding would transition at the windows and doors easily with the cedar removed. Be safe, G