Flooring - vapour block?

[Harpo]

I have some rather nice engineered Jotoba to go down soon in the hallway, study and living room.
I am going to use self adhesive foam for fixing.
The advice on the instructions is to use a PVC damp proof sheet on a concrete floor, underneath the foam.

In the kitchen and dining room I have some laminate. Again the same instructions regarding concrete.

Since my concrete floors are 20 years old, bone dry, never noticed any damp am I taking a risk in not bothering?
If there is a tiny amount of vapour coming up wouldn't it be better to let the floor breath rather than let it build up under the PVC?
I know it's no great problem just to use it and the cost isn't great so really I'm just being a lazy fecker!
So has anyone laid flooring on a seemingly dry floor without a vapour barrier and regretted it?

[Mark Benson]

We used Tuplex under our engineered oak on our (40 year old, dry) screed floor, it's made up of 2 layers of polyethylene with granules of foam similar to bean-bag foam sandwiched between them - it acts as an underlay and vapour barrier in one.
I was in a similar position to you, why bother when the floor has been down and dry for 40 years but the local timber merchant came up with this stuff and it seemed like a good idea.

http://www.tuplex.net/english/tuplex_benefits.html

[Harpo]

All in one? This stuff looks ideal. Thanks for the info and link Mark.