I have an un-insulated slab on grade home with high ceilings. I am installing hydronic radiant heat. I plan to lay down 2″ XPS then the grid of 1/2″ PEX stapled to that then pour a thin slab on that. Questions I have are: 1. Should I glue the XPS down or let it float? 2. How thick should I pour the concrete over the XPS? Thanks!
I would glue down the XPS with glue that is suitable with the materials you are using.
You should have a minimum of 1 ½” covering over the PEX.