Floor insulation - underfloor heating

Rolljet is used for impact sound insulation. Please do not refrain from using it under any circumstances. Bad idea.

An improvement of the insulation only makes sense, if at all, on the ground floor, of course. The expensive PUR stuff is actually only used if you miscalculated the heights and suddenly there's no space left for normal EPS WLG 035.

I would definitely not invest more money than necessary.

Rolljet is used for impact sound insulation. Please do not under any circumstances do without it. Bad idea.

Rolljet is nothing other than EPS with an attached foil with a grid print.

I definitely wouldn’t invest more money there than necessary.

Necessary for what? The OP has already calculated at what point it pays off. And whether it’s 10 years more or less now, the boundary has to be drawn by the OP himself. He can plan the next house earlier, but the current build height is probably set and not unusual. Expensive only on the ground floor/against the ground, good point.

It was planned correctly and on time. Combination of: Installation of the door ended up 0.5 cm too low, the screed installer a bit overly cautious, and Rolljet has worse insulation values, results in the "problem". I have now spent almost €800 more (still below the planned budget), but in return have a 0.05 better U-value instead of a 0.05 worse U-value and a clear conscience. By the way, it's all only on the ground floor. It won't go to the upper floor.

Was that clever? No idea, I'm rather stingy too, but my conscience is now clear. Cost optimizers like Nordlys would probably be tearing their hair out right now.

Rolljet is nothing more than EPS with an attached foil with printed grid.

The common insulation board under screed is of the type DEO dm (internal insulation for ceiling/floor with medium compressive strength), whereas Rolljet is of the type DES sg or sm (internal insulation for ceiling/floor with soundproofing requirements and medium/high compressibility).

The latter has an impact sound insulation value of usually 25-30db.

It is by no means the same. Please do not spread such nonsense.

Utility knife for cutting and then puzzling?

With aluminum-coated PUR boards, you won't get far with a utility knife. Get a jigsaw or a small reciprocating saw, ideally battery-powered.

I also don't really understand the purpose of the recommended PE foil. But you can simply tape the joints of the upper insulation layer; that will also create a vapor barrier.