Full rafter insulation roof or insulation on concrete slab

Is it worth it to install additional insulation between the rafters later on, even if there is already insulation on the upper floor ceiling?

Yes, did that - including a "balcony door" between the stair exit and the storage room.

What does worthwhile mean? It is not worthwhile in terms of gas consumption. It is worthwhile to really use the attic as a storage room and for hobbies. Our ship cushions for example. Uninsulated, it used to be damp up there, now in winter it is really dry up there. The Fleischmann train can now stand there, and I can play with it. Paint no longer freezes. etc. Thus, it is worthwhile after all.

What do you mean by worth it? It’s not worth it in terms of gas consumption. It’s worth it to really use the attic as a storage room and for hobbies. Our ship cushions, for example. Unglazed, they used to get damp up there; now they are really dry up there in winter. The Fleischmann train can now stay there, and I can play with it. Paint no longer freezes. etc. So in the end, it is worth it.

We just have a basement and a living area of 160m² – planned in the future are 2 children, and in about 15 years, we will probably need a little space up there in the attic for some boxes, Christmas decorations, etc.

Should I really insulate the roof for this? Honestly, wouldn’t insulation on the ceiling be enough?

we need some space up there in the attic for a few boxes, Christmas decorations, etc.
Should I really insulate the roof for this? Honestly, wouldn't insulation on the ceiling be enough here?

Let me put it this way: stuff for the flea market or recycling center doesn’t need to be cozy warm, and insulation certainly costs significantly more than a required bucket of paint. In case of access only via a pull-down ladder, one will be more selective about what even goes up there anyway.

Everyone is different....for some it's worth it, for others it would be like burning money....

The 1000€ is well-invested money, I would say! We did it too.