Ceiling height too low - lower the room

Hello there. We want to renovate our outbuilding and install underfloor heating there. Now we have a problem with the ceiling height. It is currently 190cm. The underfloor heating has a build-up height of 25cm. So the heating engineer said we should go 35cm lower than it is now to have a reasonable ceiling height. The current base is the concrete slab. Now the question is, how do we level the concrete slab again if we cut/remove 35cm from this slab? Or can someone tell me the floor structure up to the underfloor heating? Have a nice Sunday.

There are also retrofit systems for underfloor heating that require only a few centimeters of installation height.

Thank you for your answer but, we still have a ceiling beam in the middle of the room. The beam extends further into the room. If we build up any more now, I will hit my head on the beam.

You want to remove some concrete? What do you want to do with the [Bewährung]? There's a reason it's in there.

Hello, that is the question. The heating engineer just said, you go 35cm deeper here, you'll manage that on your own.

That is an effort that is not in proportion to the underfloor heating. 35cm is more or less the entire floor slab that would have to be removed.