ᐅ Structure of pitched roof insulation beneath a warm roof system

Hello,

I want to insulate my pitched roof. The house was built in 1955. In 1995, as part of modernization work, the roof was re-tiled and a so-called Thermo roof insulation was installed under the roof tiles. The attached picture is just an example to show which type of Thermo roof insulation (blue panels) I am referring to.

Now, regarding my approach:
- I would like to insulate the rafters from below using Isover or Rockwool cavity insulation. What is the most suitable option here? Which vapor barrier/retarder/membrane do I need, as far as I know, there are three different vapor membrane foils from Isover. I always thought mineral wool requires a vapor barrier...

- The ceiling below should also be insulated; it is a beam ceiling. How is the construction done here? One area is below a bathroom—does this require a separate vapor barrier installed from below? The floor structure will then be built with a 38mm (1.5 inch) particleboard.

I hope I didn’t forget anything...

Thanks and regards, Egos