ᐅ Underfloor Heating: Wet Screed or Dry Screed?

Hello everyone,

As part of a renovation on the ground floor (basement) in a sloped site, I would like to install underfloor heating. I have already removed the old flooring (strip parquet) and the screed, including the old polystyrene insulation down to the concrete slab. Now, I want to install underfloor heating in the hallway and the new children's room.

I am not sure which system I need for this. I have a total height of 8cm (3 inches) available, including the floor finish (10mm (0.4 inches)). I am currently considering what would be the best option 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 filler material to avoid voids and to prevent bending of the pipes.

Option 1:

Thin-layer system construction:

1mm (0.04 inch) foil
20mm (0.8 inch) PUR insulation board
25mm (1 inch) system board with pipes for underfloor heating
25mm (1 inch) Fermacell dry screed panels
7mm (0.3 inch) vinyl flooring
= 78mm (3 inches) total height

Option 2:

Thin-layer system construction:

1mm (0.04 inch) foil
20mm (0.8 inch) PUR insulation board
25mm (1 inch) system board with pipes for underfloor heating
28mm (1.1 inch) wet screed for underfloor heating
0.5mm (0.02 inch) foil
7mm (0.3 inch) vinyl flooring
= 78.5mm (3.1 inches) total height

Who has experience with both systems and can provide some advice?

My concerns:
Dry screed panels might not be strong enough or could squash under load.
Wet screed – exact height and drying time.

Best regards,
Bob-Bau75

For an overall thickness of 80mm (3 inches), I would use a standard traditional wet screed. Unless you require more than 20mm (1 inch) of insulation beneath the screed.

Benutzer200 schrieb:

For a total build-up of 80mm (3 inches), I would use standard wet screed, unless you need more than 20mm (1 inch) of insulation under the screed.

What about the required minimum coverage for heated screeds (45mm / 2 inches)?

Bob-Bau75 schrieb:

I would also like to install 3 empty conduits for electrical cables in the floor. These will be somewhat stabilized with dry fill to avoid cavities and bending of the conduits.

As long as they are within the 20mm (1 inch) insulation layer, that’s fine. Otherwise, I really don’t see how you can manage with the given 78mm (3 inches). In my opinion, that’s already tight to not recommended.

guckuck2 schrieb:

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

30mm (1.2 inches) is sufficient - choose the appropriate screed (from F5 grade, 30mm (1.2 inches) is enough). Using 16mm (0.63 inches) pipes on a membrane with 20mm (0.8 inches) insulation adds up to 66mm (2.6 inches). That leaves 14mm (0.55 inches) for the floor covering (or you can make the screed/insulation thicker).
Simply lay the pipes directly on the concrete slab and install insulation around them. No conduit pipes are needed.

Benutzer200 schrieb:

For an 80mm (3 inch) total build-up, I would use a regular wet screed. Unless you need more than 20mm (1 inch) insulation under the screed.

I just can’t say what would be best here; my idea was 20mm (1 inch) PUR plus 25mm (1 inch) PUR where the pipes are located. I would also like to use dry screed panels because they seem easier to handle for me.

The question is really whether there is a difference in strength between wet screed and dry screed panels.