douglas.farnan wrote:
Planning on using the fibreboard-y underlay as there a few areas with a
1-2mm difference in level and an old concrete hearth. Under the
existing floor there's about 500mm gap down to an earth solum, so will
I need any sort of damp/vapour barrier under the underlay?

If it's bumpy laminate floor won't lie properly. You shouldn't
need a DPM, but it there's any question of damp, put one in.