Insulate a concrete floor with rigid foam boards and then lay tiles on top of it?

Hello everyone,

We are renovating at home. Currently, there is a concrete floor in the kitchen and underneath it is an open space. The room below is insulated at the ceiling, but the concrete floor and the tiles are always cold.

At the moment, there are still old tiles on the floor. Now I came up with the idea to lay rigid foam boards and afterwards lay the new tiles on the boards. The whole thing is meant as additional insulation. I was thinking of about 20mm boards?

Is this even possible? Can there be cracks? What must be considered? Other ideas?

Thank you very much.

In the wall area, you can tile directly on rigid foam boards. This is not possible on floors, as the risk of damage to the tile covering due to cracks is too high. Under the tiles, you need a load-distributing board. This is usually achieved with a floating screed. You could, if the height of the floor structure allows, use a dry screed: composite elements made of gypsum fiber boards, for example, with laminated insulation. The thickness of these elements ranges between 28mm and 40mm, depending on the type of element. Example: 18mm gypsum fiber + 10mm insulation (wood fiber) = 28mm. You can safely tile on this dry screed. There are different manufacturers. You will find quite a bit about "Trockenestrich-Verbundplatten" on the internet.