Insulating the knee wall exterior: with what and how to attach?

Hello everyone!
We bought an old house built in 1960, solid construction, but completely uninsulated. Upstairs, all rooms have sloping ceilings and knee walls. Behind the knee walls there is a roof space which can be accessed from the room via a hatch.
Now we want to insulate the knee walls. From the outside, that is not towards the room, but towards the roof space. So it is not exposed to wind and weather from the outside, but to the cold roof space.
What is suitable for insulation here? Fire safety is very important to us, so Styrofoam and the like are not an option. At the same time, it should not be too expensive, because we plan to completely tear down and rebuild the house in a few years – if we have the money. But until then, we don’t want to freeze.
There are no rafters in the roof space, so it would be difficult to fix roll battens. Or should we install beams specifically for this?
The pictures show these roof spaces from the inside (and the pitiful attempts by the previous owner to insulate them; we will remove that) and the hatch from the outside.
The hatch is a problem in itself: How can it be insulated?
Oh yes: We don’t really want to use the roof spaces; the solution does not have to be constantly accessible. It is sufficient if the hatches can be opened occasionally for inspection purposes.

I would be very grateful for tips; it is already cold up there...

Many thanks and best regards
Andreas

For the roof, mineral wool is used, but just stuffing something in somewhere doesn't really earn any points.

That brings us to the second point. You will never have more money later, unless you win the lottery. Building is always getting more expensive, interest rates are rising. In 5 years, you will be able to afford less house than now. Of course, there are exceptions, like just out of university and having debt instead of equity, but that shouldn't be the case at 38 years old. It will also be difficult to get a loan at all in 5 years.

Nothing you do at this one point now will pay off in the next 10 years.

Have sauerkraut boards (cement-bound wood wool) been installed in the knee walls? How thick are the walls? I wouldn’t necessarily approach that. On the one hand, sauerkraut boards insulate quite well, and on the other hand, it would be disadvantageous to insulate only the knee walls and leave the rest of the house untreated. Whether you actually save anything then is debatable (I don’t believe so) because the payback periods nowadays range from 20 to 70 years if you follow the regulations.

Thank you very much for the quick initial responses! The situation is that we currently only occupy the upper floor. And it is already cold and drafty there at night, especially for my wife and child. Hence the intention to insulate. It is not about amortizing the costs, but about creating quality of life. The thing with the Sauerkraut boards is true, but only on one side of the house. I don’t have a photo of the other side at hand right now, but in any case, only the bare masonry can be seen there. The walls are about 20 to 30 cm thick. But even where the Sauerkraut boards are installed, the problem with the shutters remains. And everywhere there are cracks and gaps where you can clearly feel the drafts. I would therefore be very grateful for further suggestions! Best regards Andreas

On the upper floor, all rooms have sloping ceilings and knee walls. Behind the knee walls, there is an attic space, which can be accessed from the room via a hatch. Now we want to insulate the knee walls. Specifically from the outside, meaning not from the room side, but from the attic side.

Correct terminology is extremely helpful to avoid talking past each other. Normally, this is more of a nuance for me, but here is a special case where both apply simultaneously, so the terms should be separated:



If I understand correctly, you want the insulation where the yellow foam is shown on the attic side of the knee wall in the picture. You want to leave the knee wall itself untouched, which I also consider sensible.