Attic interior insulation - Roof already starts at the upper floor

Hello everyone,

this has probably been explained 1000 times already, but I can't really find anything about it. I want to renovate and insulate the attic. That means removing the wooden cladding, taking out the old thin insulation, putting in new thick insulation, and covering it with drywall. That's no problem in the attic so far. However, the roof already starts in the upper floor. I am assuming that I can't really push the materials down from above. How do you proceed in this case? I would rather not remove the sloping walls in the upper floor to get behind them. Insulating from the outside, i.e. removing the roof covering, is also not an option for now. Can you give me a tip?

Thanks to you.

There is also injection insulation, maybe that is an alternative? But I am not sure if you can achieve such good values with it as with "normal" [Zwischensparrendämmung].

Hello everyone,

I had a roofer here now. He told me that I should remove the wooden cladding in the attic. Then I can double up the rafters up to the attic floor and then insert additional insulation into the rafters. The insulation is therefore thicker from the attic floor (20 cm). In the upper floor, the insulation is only 10 cm.
The only important thing is that I cut the aluminum foil on the old insulation before I put the additional insulation on.

In case someone faces the same problem, I just wanted to briefly share my solution here.