As an independent flooring inspector, I have always said how important it is to check the subfloor to guage its moisture content. If you do not do this at the onset it may very well come back to haunt you.
The customer may well think that the subfloor is dry enough to lay the wooden floor on with a simple vapour barrier, because the builder has said that there is a damp proof membrane installed under the screed.
As a flooring contractor you must be strong and insist carrying out a moisture test and if the rh reading is above the magic 75% insist on installing the appropriate Damp Proof membrane.
Liquid Damp Proof Membrane
Sandwich Damp Proof Membrane
All too often, I am called as a flooring inspector to look at failed or discolouring flooring.
Picture of discoloured floor
Most of the time the floor is failing as a result of high moisture
content, usually coupled with an inadequate Damp Proof Membrane.
As a professional independent flooring inspector, I urge all you contractors to be stronger and insist on installing a suitable Damp proof membrane.
If not, then ultimately when the floor fails it will be your ghost that comes back not just to haunt you but burn a big hole your pocket.