Alan Morris
Hi Gerard the thickness of the underlay is determined by whether the subfloor is concrete or wood and what condition it's in if it's chipboard and in good condition you can get away with the 3mm foam if it's floor boards and a bit up and down you can use fretboard which is 5-6mm if it's concrete I would recommend a 5-6mm underlay with built in damp proof layer. I hope this helps . Alan
