Extension of the screed opening. Can this screed break?

In your case, I would have installed a plinth at the necessary height in the composite (to the raw ceiling), where the fireplace will then be placed.

Do I understand this correctly: ... the raw ceiling is built higher up to the top edge of the screed under the fireplace base area?

Yes, that is correct. The adjacent top layer is then extended up to the base area of the fireplace to provide a clean visual finish. The load transfer via the base onto static floor slabs or story ceilings is also common in commercial construction or with [Großküchengeräten].

For me, summarized, I take from your answers that it is not visually appealing and that perhaps it would have been generally better to proceed differently, but with regard to our project (intensively described above) it does not mean any real restrictions, right?

No, not right! The appearance, which is brought to the forefront here, plays no role at all later on! The recess was too small, it was enlarged. The chimney is placed on the raw ceiling in a composite manner via a base made of cement screed and separated from the floating screed by a joint. Then the top layer is laid up to the chimney and the conversion is finished. Functionally and visually flawless! No one lives directly on a screed. It will be plastered and covered with a top layer anyway. There are no problems! If the chimney had been built on the floating screed, well then the situation would have looked completely different!! ---------------- Memorandum: Problems arise, you recognize and solve them. Only those problems that are talked into existence are often unsolvable and usually swell inappropriately. Regards: KlaRa

Hello KlaRa,

thank you for your feedback and your explanation of how you would have done it/how it would have been correct from your perspective. But what do I do with that now? It is currently the way it is. What is your assessment of the above described?

Regarding:

Der Kamin wird im Verbund über einen Sockel aus Zementestrich auf die Rohdecke gestellt und durch Fuge vom schwimmenden Estrich getrennt.

We were told that omitting the insulation is not possible because it would create a thermal bridge. Be that as it may – see question above: What is your assessment of the described work? What exactly do I do now?

Best regards,
Seol

The chimney is installed in connection over a base made of cement screed on the raw ceiling and separated from the floating screed by a joint.

So alternatively to thickening the raw ceiling in this area, the raw ceiling is normally thick and on top a cement screed, just not floating, but directly on the raw ceiling?

We were informed that omitting the insulation was not possible, as it would create a thermal bridge.

I don't see that, since a separating strip is placed towards the floating screed (?)