What is a vapour barrier? And more importantly, why do you need it?
Vapour barrier is simply described as a diaper for your flooring, but it’s not really for your flooring and I guess it’s not really holding anything in, it’s more for keeping stuff out. So I guess a vapour barrier is better described as a sheet of plastic (sometimes attached to a foam underlayment) that is used to protect your new floor against moisture from your installation surface (in most case, concrete).
Concrete has a bad habit of sweating. (So do I, if you want the truth!) When this happens, the vapour barrier acts as a protective sheet against water penetrating or impregnating your finished flooring surface.
Basically, as a simple rule of thumb, if you’re installing flooring over concrete, you should use a vapour barrier. There are exceptions to every rule of course, so if you’re in doubt, contact a licensed contractor or flooring expert (like me) to give you the full low down on your sub floor requirements prior to flooring installation.