Old building: Retrofit underfloor heating on the upper floor?

I would also take a look there, because depending on the thickness of the insulation layer, it might be possible to do something without the height changing significantly, as there are very thin heating systems. I would definitely not mill into the concrete ceiling, but you might need the structural engineer for the screed if the floor construction has been very light so far.

Hello everyone, Today we sawed open the floor in one spot. It is actually the case that there is an insulation layer made of mineral wool on the concrete slab and on top of that about 4cm thick chipboard panels have been laid. The carpet was then glued on top. In total, there is a height of 14cm, which should actually be enough for underfloor heating.

At 14cm you can fit almost anything, such as wooden beams with dry screed and underfloor heating, on top of which you can then nail floorboards or use OSB with carpet/vinyl, etc. Or if the structural engineer agrees, also Styrofoam plus screed and in the latter the underfloor heating.