Insulate basement floor and install underfloor heating

In my newly acquired single-family house built in 1985, I want to insulate the basement floor retrospectively and install underfloor heating. There is a screed without insulation. The screed was poured directly onto the concrete floor. I now want to break this up. The concrete basement floor underneath is uneven. Now my questions about the new construction.... 1. Do I have to level and seal the uneven floor? The floor or the existing basement is dry. But I have heard that if you install underfloor heating retrospectively, the floor can then absorb water (or condensation)??!! 2. My plan would be to lay a 10 cm PU insulation on the existing floor - lay the underfloor heating system on top - then screed over the whole thing. What is the correct construction or procedure here?

We installed underfloor heating as part of a renovation. Since not everywhere has a basement, the build-up over the floor slab was as follows:
Leveling compound
6cm insulation
Dry screed boards
Retrofit underfloor heating
Screed/leveling compound
Tiles

Do you have enough room height?

Good morning, yes, room height of about 2.60 m is sufficient. Can't the underfloor heating be installed directly on the insulation? That would reduce the overall height... thanks and best regards

To my knowledge, no, because the insulation cannot withstand the pressure. There must be another layer in between for load distribution. Our structure cost almost 15 cm in height.

2. My plan would be to lay a 10 cm PU insulation on the existing floor - install the underfloor heating system on it - then screed over the whole. What is a correct structure or procedure here?

I would lay a Katja membrane on the existing floor for sealing (by the way, this also helps against radon, although whether this is necessary/useful depends of course on the residential area, a look at the "radon map" helps). Then PUR insulation -> thin stapler plates -> underfloor heating system with screed -> floor covering.

Whether leveling compound on the concrete floor is necessary beforehand can only be decided on site - small unevenness can be compensated by the insulation - not a 3 cm height difference from left to right corner of the house.

As far as I know, no, because the insulation cannot withstand the pressure. There must be another layer for load distribution in between.

I suspect there was another reason, because the usual floor insulation boards & underfloor heating fixing plates are already specifically designed for the load distribution of the screed to be applied above. Additional dry screed is not necessary in the standard construction.