Insulation under reinforced concrete floor slab KFW55

The price has one zero too many. If insulated under the slab, you can save on top of it or make a combination of both.

ok, then I should first find out exactly what is between the floor slab and the parquet.

Otherwise, I could also ask the construction company that pours the floor slab what it directly costs them.

The price has one too many zeros.
If insulated under the slab, you can save on top or do a combination of both.

Can you explain to me as a layperson what the advantages are?

Thank you very much and best regards

Advantages are not only that overall the insulation should be right. Otherwise, you get cold feet or, which I find much worse, you end up heating the sand in the ground.

And such an air-water heat pump relies on good to very good insulation. My question was more about the transmission medium, that is underfloor heating or radiators. But the question has also been answered.

ok, then I should first find out exactly what is between the base slab and the parquet.

Maybe I could also ask the construction company that pours the base slab what it directly costs them..

Can you explain to me as a layman what the advantages are?

Many thanks and regards

Insulation under the slab is free of thermal bridges, which cannot be said for exclusive insulation on the slab or the combination of insulation on/under the slab. In my opinion, this is theoretical in nature.
The "disadvantage" of exclusive insulation from below would be the building component activation, meaning you are also heating the slab because the underfloor heating is not insulated against the slab.

Ultimately, you will take the system that is offered to you at the most favorable price. And that is also okay.

so above the base slab there are 6cm insulation, 2cm tack board, 5.5cm screed

I think that is very, very little and would definitely change something. You never get access again and because of the underfloor heating, the losses are also relatively high.