Kniestock insulation, ceiling beams pass through masonry

Hello everyone,

I am new here and hope you can help me.
We are currently planning a new roof structure (80-year-old house). The old roof has water damage, and for a stairway, the roof is to be raised by 50 cm (knee wall). The building permit is available.

It is currently a hip purlin roof. And it will also be a hip purlin roof again.

Boundary conditions:
- The ceiling beams are embedded in the wall and protrude outside the wall.
- The facade was insulated with Styrofoam several years ago.
- The roof is to be fully insulated with wood fiber: 24 cm between the rafters and 8 cm above the rafters.

Question:

How is the insulation around the knee wall best solved?
1) Place the vapor barrier on the ceiling beams (marked in blue) --> risk that draft passes by the ceiling beams protruding outside and moisture settles on the ceiling beams?
2) Try to seal the ceiling beams in the wall?
3) Completely fill the roof box with insulation? Is ventilation necessary?

So far, the area is very well ventilated; somehow I am afraid that if I seal it so tightly, it will start to rot.

By now I am somewhat desperate. What is your opinion? How should the insulation concept look here?
I would really appreciate your suggestions.

Best regards
Daniel

If the attic is converted; how should we imagine the future thermal envelope (I am only puzzled by the question relating to the wall penetration)?

Thank you for the inquiry.

A new roof truss will be installed on the roof, which closely resembles the current roof truss. However, it has wider rafters (24 cm) and a knee wall of 50 cm. With insulation between the rafters and above the rafters (24+8 cm), the attic will be converted into living space. So the concept is basically set.

The only open question:

What is the best way to seal the knee wall, especially in connection with the ceiling beams passing through the masonry to the outside?
Should slots with insect screens be made at the roof box for ventilation?