If the thermal insulation layer is on a concrete plate, then it can be made of ordinary polystyrene plates or from hydrophobic, solid minvata of high density and strength. Despite whether we use mineral wool, or extruded polystyrene foam, the thickness of the thermal insulation layer should be at least 10 cm. In the case of mineral wool, it must be remembered that it is separated on both sides of other layers using waterproofing. Choosing polystyrene foam, it is better to take with fixed joints that allow you. Thanks to this, the risk of the formation of cold bridges will be much less.