Insulation under screed in old building renovation with underfloor heating - experiences?

Hello dear builders,

I live on the outskirts of Munich and am currently renovating my grandparents' single-family house from the 60s. The entire floor is being redone with screed and underfloor heating. The old screed and insulation have already been removed. The build-up height of the old floor was about 8 cm. To avoid problems with the doors/balcony windows, the new floor should, if possible, not be more than 10-12 cm (i.e., 2-4 cm more than the old one).

I have received an offer from a heating engineer, and I do not know how to evaluate the following components.
The offer includes the following insulation, which is supposed to be laid stacked under the underfloor heating, and this combination seems unusual to me. This is to be installed both on the ground floor (uninhabited/unheated basement) and the floors above. No further insulation material is included in the offer.

- Steinwolle TP impact sound insulation 5kn/m 13-3mm des skr 0.63 mk/w
- Mineral fiber impact sound insulation 3.5 kn/m2 20-5mm mw 035 des smr 0.37 mk/w

Internet searches have not helped me so far. I am currently stuck here and would be very happy if someone could explain what this is and whether this combination is usual or whether there are better options for me.
Of course, I will also speak with the heating engineer, but I would like to gather more information in advance if possible.

Many thanks in advance!
Andreas

Rock wool TP impact sound insulation 5kn/m 13-3mm of the skr 0.63 mk/w

Rock wool = material (harder than glass wool)
TP = TrittPlatte impact sound insulation board (manufacturer's abbreviation, presumably Knauf?)
5kn/m² = load capacity (here approximately 500kg per square meter, thus more than a usual screed)
13-3mm = thickness of the board and maximum compression. The board is 13mm thick and can be compressed under load by up to 3mm.
DES = abbreviation for the application area of the respective insulation boards. Here "internal insulation of the ceiling or floor slab under screed with impact sound insulation requirement."
SK = denotes the "compression class". However, to my knowledge there are only "sg", "sm", and "sh" (low, medium, and high), is the "K" a typo?
R = R-value is the reciprocal of the U-value and indicates the thermal resistance.
0.63 m²*K/W = R-value of this insulation board (although this value does not seem correct to me)

Whether this construction is common, I unfortunately cannot answer due to lack of experience. However, I have been told that mineral wool as insulation under screed is not necessarily ideal because it is generally too soft. This may then lead to permanent sagging of the screed with corresponding consequences for skirting boards and/or tile joints at the wall-to-floor transition.

In general, I would first ask myself why this construction should be used in the ground floor above the unheated basement. On the one hand, there are more effective solutions (e.g., PU boards) that provide significantly better insulation values, and on the other hand, there is no need for impact sound insulation towards the basement floor.

As for the installation height: Have you considered the rise of the first and last step of your staircase? If the new floor is 4cm higher, the step height decreases and the staircase could possibly become a tripping hazard. According to DIN, a maximum deviation of 15mm at the first and last step is allowed.

That is not insulation at all, just impact sound insulation. However, there should be proper insulation under a floor heating system. Depending on the available build-up height, this can be very well achieved with a dry construction floor heating system (including screed, total build-up height 4.5 cm) plus the insulation. With 8 cm, that would leave only 3.5 cm, so that the same floor level is ultimately achieved. The best option here would probably be a 2 cm vacuum insulation panel (I believe it has 0.07 W/mK), and I would plan the remaining 1.5 cm for floor leveling. Since the floor heating system panel is also 2.5 cm EPS, the insulation is more than sufficient.

Many thanks for your quick and detailed responses!

I didn’t know if it was relevant, but on the insulation there is PE screed foil and a Praski Bavaria Biofiber perforated board (which also doesn’t seem to be standard), onto which the pipes of the underfloor heating are clipped. Above that, anhydrite screed. The flooring on the ground floor and first floor will be tiles, and in the attic laminate or vinyl.

Exactly the missing thermal insulation I had feared. Would an alternative to insulating the ground floor be insulating the cellar ceiling? Unfortunately, I only have limited space here because of the low cellar ceiling (2-3cm). I will take a closer look at the suggestion of a vacuum insulation panel.

Thank you very much! Andreas

Of course, you can also attach the insulation board from below (to the basement ceiling), but this does not prevent most of the heat from flowing downwards (into the ceiling slab). The partition walls will then also be heated, whereas with insulation from above you can somewhat counteract this with the edge insulation strip. If the heating company's offer has not yet been signed, it may be worthwhile to obtain an alternative offer that includes insulation from above.

The monetary effort for vacuum insulation panels is unlikely to be in any proportion to the possible energy savings.