Then you do not count from the raw floor but from the top edge of the floor to the top edge of the floor of the next story. It does not matter whether it is screed or finished floor.
The insulation between the floors in the single-family house I find crazy.
Oh, is that so? But if the living room is always kept at the same temperature level and the bedroom above cools down at night, insulation suddenly makes sense. I don’t want to cool the cool bedroom from below. And in summer, the heat from the upper floor doesn’t penetrate downstairs so quickly.
That makes much less difference with a few degrees of temperature difference than you think. Insulation relies on a large Delta T. Inside 22°C, outside -10. That makes sense... but not with 21°C living room to 18°C bedroom... Especially since the heat finds its way anyway through air exchange, through the interior doors, through the walls, through the staircase.
The insulation under the screed is not only meant to maintain a temperature difference. It is also intended to direct the heat from the underfloor heating in one direction. Otherwise, you could just as well install the heating in the ceiling cavity and save yourself all the hassle.
That is unfortunately complete nonsense. The insulation serves to prevent heat loss through the concrete. That makes sense when insulating towards the outside, where the temperature is traditionally lower than inside the house. For example, with the floor slab. But insulating rooms or floors against each other within the thermal envelope is pointless due to the small temperature differences.
Of course, there is temperature equalization within the thermal envelope, but with that argument one could also stick to a single heat source in the kitchen, like in the old days. It is more efficient if the heat is directed specifically to where it is needed. Otherwise, more underfloor heating surface might be required there.