Upper floor too low, is insulation possible without loss of room height?

My husband looked at a house in the neighborhood today. It is being sold privately ([Erbfall]). We somehow don’t have very exact information yet (the year of construction is around 1930). The plot is 1000 sqm, a final plot that cannot be built on. Oil heating, gas should be in the street, the electrical system is still uncertain, but at least the fuse box is already new. Copper pipes are installed. All rooms are pretty small. Estimated living area is about 100 sqm. The basement has a very comfortable room height of about 2.70m. The upper floor was converted later, and that’s where the problem lies. The room height there is only about 2m, so basically not living space, right? The roof was covered with wooden shingles about 15 years ago, and that on top of the existing tar paper. Upstairs there are two rooms each with two “Abseiten” and in the middle a tiny toilet and a small gallery.
In theory, one could remove all the drywall partitions and reshape the rooms upstairs. But we have to install insulation according to the energy saving ordinance, right?
That means we couldn’t really use the upper floor except as storage (which was originally planned anyway)? I’m currently out of ideas. But I suspect you would need to know how the roof structure is built for that?
There are more issues that would need attention in the house, but the substance makes a good impression, the neighbors are nice, and the price is completely within our means with enough leeway to invest a few more euros. Basically, though, you could move in right away.

Let's be honest: You don't buy static numbers, but living space. It is completely irrelevant what ceiling height is where or anything else. Either you like it or you don't.

Let's be honest:
You don't buy static numbers, but living space.
It is completely irrelevant what ceiling height is where or what. Either you like it or you don't.

That's true. But we would need the space upstairs as living space. If we had to reduce the height to insulate, it would just become too low. It's already quite cramped as it is. I'll upload some pictures tomorrow that I have received.
We actually want to open up the knee walls to maybe build in wall cabinets.
I haven't seen it myself yet. I'll do that next week.

Then it's simply not yours and you don't buy it. It's not about numbers, it's about feeling - either it fits for you or it doesn't. You can post as many photos as you want: I like it, doesn't ;)

I haven't seen it myself yet. I'll do that next week.

You are absolutely right in your assumption; for more than coffee ground reading, one would need more than the above text description.

Completely redo the roof structure and raise the roof by half a meter? From about 60,000 upwards, that is feasible. Then you also have everything up to the new standard upstairs. Does [der Bebauungsplan] allow that?