I only have about 75mm of thickness to work with, but i want to put wet system under floor heating in my kitchen, then tile over it. I want to use flow screed, to cover the pipes above the insulation which will be laid onto the concrete sub floor. I understand that you can get 10mm insulation boards for the very purpose of low profile under floor heating, and in my case i think i may get away with 20mm? But my biggest concern is building regs, will i get away with thin insulation? I dont want to open a can of worms by asking my building inspector until i get some advice from here.