The required screed thickness depends on the type of installation, the screed material, the use (live loads to be applied as single/surface loads) and the thickness of any existing insulation layer. Taking these dependencies into account, the required screed thickness can be found in the relevant part of DIN 18560: Part 2 for screeds and heated screeds on insulating layers, Part 3 for composite screeds, Part 4 for screeds on separation layer and Part 7 for heavy-duty screeds (industrial screeds).
Source: bauwion
