Screed necessary? Unfinished but insulated attic

Underfloor heating on the ground floor and upper floor.

Then there should also be insulation on the ceiling between the ground floor and the upper floor so that the underfloor heating of the upper floor effectively heats the upper floor and not the ceiling it rests on. I guess that's how it is for you as well.

I agree with #17 and #18, as I already asked about the ventilation concept in #14. And again the question: How/where is the airtight envelope implemented? Identical to the insulation (would be normal)?

With a storage room roof, the top floor ceiling is the more sensible boundary surface.

Of course, that depends on whether you want the storage room to be frost-free. Outside the insulation, it is not frost-free.

Consistent would be: screed plus heating and especially a fixed staircase.

Okay, thank you for your opinions.

Consistent would be: screed plus heating and above all a fixed staircase.

That is correct if I were to use it as permanent living space.
The primary purpose of the attic is storage space, but I wanted it to be frost-free.
The second purpose will be to install some climbing holds and train there.

Therefore my plan is to insulate the roof right away so I don't have to start with that later. Heating and a fixed staircase are not necessary for this purpose, and in my opinion, neither is a flat/pleasant floor (screed).

But that means I will reconsider insulating the floor to the upper floor with wool.

Thank you very much for your support.

BER in the sense of differently meaningful): the insulation should not be surrounded by the environment, but separate warm from cold. For a residential roof, the insulation of the outer shell would be favorable, for a storage room roof the top floor ceiling is the more sensible boundary

That’s exactly how the architect explained it to us as well: if we want open ceilings, then the roof is insulated; if not, then the top floor ceiling.

In your case, it simply was not implemented sensibly. So now you are heating the attic as well.

That’s exactly how the architect explained it to us as well: if we want open ceilings, then the roof is insulated; if not, then the top floor ceiling.

In your case, it’s just not sensibly done. So now you are heating the attic as well.

That it heats the attic as well is completely irrelevant. How much greater is the heat loss compared to the version with an insulated top floor ceiling? 2%? Totally insignificant. Otherwise, I agree with 11ant, screed and insulation on the top floor ceiling only have a minimal effect and at the same time have the disadvantage that you then lack the construction height in the attic.

Where do the 2% come from? Did you calculate that?

Estimate by how much the total surface area of the building envelope increases, and then roughly subtract some amount