Underfloor heating: Wet screed or dry screed?

Hello everyone,

In the course of a renovation on the ground floor (basement) in the hillside, I would like to install underfloor heating.
Now I have removed the old flooring (strip parquet) and the screed including the old Styrofoam insulation down to the concrete slab.
Now I would like to install underfloor heating in the hallway and the new children's room. Unfortunately, I am not sure which system I need for this.
I have a total height of 8 cm available including the floor (10 mm).
Now I am somewhat considering what the best option would be for the ground floor.
I would also like to lay 3 empty conduits for electrical cables on the floor. These will be somewhat stabilized with dry fill to prevent hollow spaces and bending of the pipes.

Option 1:
Thin-layer system structure:

Foil 1mm
20mm PUR board
25mm system board with pipes for underfloor heating
25mm Fermacell dry screed boards
7mm vinyl floor
= 78mm total height

Option 2:
Thin-layer system structure:

Foil 1mm
20mm PUR board
25mm system board with pipes for underfloor heating
28mm wet screed for underfloor heating
Foil 0.5mm
7mm vinyl floor
= 78.5mm total height

Who has experience with both systems and can give a few tips on them?

My concerns:
Dry screed boards might possibly not be that load-bearing or might compress.
Wet screed exact height and drying time.

Best regards

For an overall construction height of 80mm, I would use regular wet screed. Unless you need more than 20mm of insulation under the screed.

With an overall build-up of 80mm, I would take normal wet screed. Unless you need more than 20mm insulation under the screed.

What about the required minimum coverage for heated screeds (45mm)?

I would also like to lay 3 empty conduits for electrical cables on the floor. These will be somewhat stabilized with dry fill to prevent hollow spaces and bending of the pipes.

As long as they are in the 2cm insulation layer, okay. Otherwise, I really don’t know how you want to manage with the given 78mm. In my opinion, already a stretch to not recommended.

What about the required minimum coverage for heated screeds (45mm)?

30mm is sufficient – choose the appropriate screed (from F5 upwards, 30mm is enough). Add 16mm pipes on foil and 20mm insulation, totaling 66mm. That leaves 14mm for the floor covering (or you make the screed/insulation thicker). Simply lay the pipe on the concrete floor and put the insulation around it. No conduit pipes.

For an 80mm total build-up, I would take normal wet screed. Unless you need more than 20mm insulation under the screed.

I just can't say how much is best, my idea was 20mm PUR + 25mm PUR in which the pipes lie. I would also like to use dry screed panels because it is easier for me to handle (I think).

The question is actually whether there is a difference in strength between wet screed or dry screed panels.