20cm 035 plus additional styrofoam with underfloor heating?

Morning,
I am currently renovating a house. We will install underfloor heating on the first floor. Between the first floor and the ground floor we have installed 20cm 035 glass wool (between the beams) (there is no heating planned on the first floor - it is basically a garage or storage room). On top of that came OSB boards. I just found out that now 14cm will be added on top of the OSB boards, namely Styrofoam insulation, impact sound insulation, underfloor heating and of course screed. I think the finished surface is also included in that - but I am not sure.

My question - do you really need the Styrofoam insulation if you already have 20cm insulation under the OSB? I don’t want to save on insulation - but I also don’t want to overdo it if it doesn’t help. Or is it simply impossible to lay underfloor heating directly on OSB (or directly on mats on OSB) without some insulation underneath?

CF

Hello,

.... We will install underfloor heating on the first floor. Between the first floor and the ground floor, we have installed 20cm 035 glass wool (between the beams) (no heating is planned on the first floor - it is basically a garage or storage room).

....- but I'm not sure about that.

With such expenses, one should always be certain!

.My question - do you really need the polystyrene insulation if you already have 20cm insulation under the OSB?

Here, the Energy Saving Ordinance §9, Annex 3 must also be observed.
However, an additional 14 cm seems a bit excessive. The inventor of the measure should be able to provide a justification!
With dry screeds and insulating floor coverings, more insulation is required below the heating layer compared to wet systems.

Underfloor heating must be carefully dimensioned if it is to provide comfort and be energy efficient.

Best regards.

Thank you for the quick response. What I meant by 14cm was 14cm including the screed. I am not sure how thick the Styrofoam boards will be that are laid directly on OSB - I estimate about 6cm. The finished floor height should therefore be (at least) 14cm above the OSB boards. That would be 20cm 035 underneath, 22mm OSB, probably 6cm Styrofoam, and then pipes and screed (possibly other layers - e.g. impact sound insulation).

So I gather from the answer that additional insulation above the OSB is not only sensible but necessary - that is reassuring :-)