ᐅ Experiences with Thin-Film Underfloor Heating Systems

Hello everyone, does anyone have experience with thin-layer underfloor heating systems?
I have a limited floor construction height (8 cm (3 inches) above concrete, including flooring). In my partially underground ground floor, where there will still be about 3 cm (1 inch) of insulation, this leaves around 3-4 cm (1-1.5 inches) for the underfloor heating. On the main floor, the height is not so tight since no insulation is needed, only impact sound insulation (if at all). I have obtained quotes from 2-3 companies. Two quotes are for thin-layer systems with special screed (both require only 2 cm (0.8 inches) above the underfloor heating pipes), one is for a dry construction system (total underfloor heating height 2.8 cm (1.1 inches) – but the modest concrete slab would need to be well leveled), and one for liquid EPS screed. Plan B would be to forgo underfloor heating and continue heating with radiators, but replacing them with low-temperature models. Plan B costs half as much, but it would be frustrating to renew all the screed without installing underfloor heating. Thanks.
P.S. If anyone has insulated or renovated on a ground-level concrete slab using PUR/PIR, it would also be interesting to hear how well it worked.

paulch7 schrieb:

P.S. If anyone has insulated or renovated with PUR/PIR on a slab-on-grade foundation, it would also be interesting to hear how well it worked.

Not on a slab-on-grade foundation, but on a basement ceiling (and about 20cm (8 inches) into the basement). The floor wasn’t perfectly level, but that didn’t matter to me. I applied PUR, stapled the underfloor heating directly onto the PUR, then added a very thin screed layer on top. It worked perfectly. Are 20mm (0.8 inches) of insulation in the basement ideal? No, but both my energy consultant and I don’t see it as a real issue.

paulch7 schrieb:

Plan B costs half as much, but it would be frustrating to have to replace screed everywhere and not install underfloor heating.

Exactly right. Better to sacrifice one centimeter of insulation and plan the underfloor heating with a 5cm (2 inch) pipe spacing if necessary, so you can run it at a low supply temperature. This can be calculated.

Swisspor PIR Premium 0.018 or Bauder WLG022 are currently unavailable anywhere, which is worrying me.
What also concerns me are the blue drops in the Ubakus calculator, probably due to the water vapor diffusion resistance factor.
An alternative could be Foamglas boards, but their insulation performance is not as good. I even looked into Spaceloft Aerogel but am unsure if it is suitable for floors (strength). What is appealing about the Turbolight screed systems is that, in theory, you could install standard 16mm (5/8 inch) underfloor heating pipes.

What do you need 10mm (0.4 inches) aluminum foil for? You already have aluminum-laminated PUR foam.

I thought a vapor barrier (aluminum-bitumen) is necessary to prevent any moisture (condensation) from being released. It is currently installed under the old screed. For foam glass, it would be overdue, but unfortunately, the U-values of foam glass at the same thickness are twice as poor as those of PIR.