Rafter insulation with Armaflex?? Question!!!!

That means the cross beams will then form the new ceiling? The ceiling goes on these beams and on this, the insulation. So you would retain the cold roof and only raise the ceiling itself a bit higher?
Your critical points would then be the slopes from the ceiling down to the floor/knee wall?

Then it would probably be less dramatic to realize, although I don’t know how to neatly finish such a segmentation, i.e., with the vapor barrier.
You can probably find a professional through Google; otherwise, I wouldn’t know either.
I asked the local roofer back then and subsequently obtained material through him.

I’m also just a DIYer without professional training, so I can’t give you precise statements.

So the crossbeams then form the new ceiling? The ceiling goes on these beams and on top of that the insulation. So you would keep the cold roof and just raise the ceiling a bit higher?

Not quite, there shouldn’t actually be any ceiling anymore, that’s the problem. It wouldn’t be a cold roof anymore. The rafters should remain completely visible, only the roof slope should be clad all the way up...

Then you should be able to create ventilation between the formwork and insulation using spacers. However, due to the thickness of the construction, hardly any rafters would be visible. The only option would be a fake rafter, which sure also looks good. An alternative would be an external roof insulation. But then there should be no attic/loft anymore and the ceiling up to the ridge purlin would have to be removed everywhere.

In this case, there is really no way around a surveyor/expert.

Then you should be able to create a ventilation gap between the formwork and the insulation using spacers

Ventilation will be difficult anyway, since the lower part of the roof is sealed. Today, the ventilation is implemented through the holes in the wall.

In this case, there is really no way around a surveyor/expert

It is a good way

Ok, thanks for the many answers. I will take care of finding a specialist, everything else is just too hot for me.....

Best regards Kevin