Retroactive roof insulation with crawl space

Hello,
my name is Torsten and I am new here.

We recently bought a single-family house built in ’65. After the initial restoration work and moving in, I am facing the following problem/question.
Our house has an upper floor with crawl spaces on the left and right. The roof still looks good, but it was not insulated; I would like to catch up on that. Of course, there is no underlay membrane, so I wonder if there is a solid way to insulate the roof without an underlay membrane? Or if that makes no sense: Would it make sense to insulate the walls of the rooms and the ceiling of the ground floor in the crawl space? The part where the rooms from the upper floor reach up to the roof was apparently insulated. How exactly, I can't say; I haven’t opened it yet.

Regards and have a nice weekend!

The section where the rooms from the upper floor reach up to the roof has apparently been insulated.

If I understand correctly, it concerns knee walls partially accessible as storage rooms – in that case, I would indeed probably install the insulation on the floor (and on the knee walls) – as well as partly rooms with open roof undersides. Pictures – possibly also the sectional drawing – would be helpful for further details. Is there a third type of room (with an attic above) as well?

Here are a few pictures of the situation.

Just sketch the floor plan as well.

Something like that

Where are the passages to the storage rooms, and what do you want to use them for?

The section where the rooms from the upper floor reach up to the roof has apparently been insulated. How exactly, I can’t say, I haven’t opened it yet.

I suspect insulation that no longer corresponds to current practice. You can still leave it as it is, but you should then continue "similarly poorly" next to it to avoid creating thermal bridging differences between adjacent areas.

Unfortunately, I am not an expert in this field and therefore mostly limit myself to asking you questions to draw out more details, to which others can hopefully then offer "recipes."