Styrofoam granulate at different raw building floor heights

Phew, I would think twice about such a hassle for a dry system, especially with the background thought of underfloor heating.

I would continue to use either only pressure-resistant insulation boards or in combination with loose fill. Possibly pay attention to relief joints or inserts. The costs for the additional insulation should remain reasonable for the shown area.

I see no advantage of a dry system here, but some disadvantages.

I see.... I don’t know the size, next to it there are more rooms, so depending on the private situation, the costs would at least be one of the parameters, plus the own handyman skills, which are limited in my case. But in general, I agree with you that insulation boards would be a good approach, but I was more thinking about the quantity of the other rooms with 28cm each, because 28cm insulation boards.... at some point there is a limit. What problem would you see with underfloor heating or what disadvantages do you mean? One likes to learn.... If a professional company does it and not DIY, I would have it done the way it is recommended to me anyway. Added to that is also the type of use of these rooms......