I've read your guidance on installing over 2 types of subfloor. In our case most of the floor is newly laid concrete with two areas of wood floorboards. You suggest a dpm over the concrete and then hardboard over the whole area. What thickness of board & what type (?ply) do you recommend? How should it be fixed?
We're concerned about the overall thickness of the floorcovering, it is the hall with five doorways off, with four different floorcoverings on the other side.
All depends on if you plan to install the wooden floor ongoing (i.e. without thresholds in between the rooms).
Is so, thin sheets of hardboard (3mm) would be sufficient.
If you install all areas as different rooms i.e. using thresholds in between then you use one type of underlayment for those rooms containing concrete (with DPM) and another type for rooms with the existing floorboards (foam underlayment)