Vapour Control Layer on a flat roof. Stop interstitial condensation

Time and time again I see the wrong vaper control layer being used and installed incorrectly. Interstitial Condensation can happen if warm air from inside the building gets up and into the roof structure. Interstitial condensation only occurs if all conditions are correct but when it douse the problems can be immense. Interstitial condensation not only happens in the flat roof but can happen anywhere on a building where all the conditions are correct. The issues I see are mainly because of the lack of attention to details, bad workmanship and bad specification of materials.
Interstitial condensation is known outside the trad under several different terms such as "sweating in a roof" "Condensation in a roof." Is now becoming a very big problem