Vapour barrier underlay upstairs?

Silence101

We've been looking at the vapour barrier underlay we need to put on the concrete floor downstairs, but from what I see we need 31sqm which means that we'll end up between 9 and 14sqm spare once we've put it down. (Rolls are either 10sqm or 15sqm) Can we use the left over upstairs/on the stairs, or will it end up damaging the boards, by trapping the moisture in them? It's a new build so I'm pretty sure we'll definitely need it downstairs.
Thanks .

Marb6145ky

From what I see, Underlay 4 u offer this in individual square meters. Saving waste. On another note, you should really buy a little extra for wastage - usualy between 5 and 10%

armchaireconomist

Why do you need a vapour barrier?

Furts

armchaireconomist wrote: »

Why do you need a vapour barrier?

Likewise. On a ground floor slab of a new build the slab should be allowed to dry out before it gets sealed over. I picture Tredaire type underlay as breathing, less so modern foams. Seems to me condensation and mould issues could arise. You do not want a barrier that traps the moisture in the slab.

armchaireconomist

Did not mean my previous post in an accusatory way, just interested as to why you need one for your new build. As mentioned above, depending on how "new" it is, concrete can take months to fully cure and you don't want to seal it. Otherwise, I can't see much purpose unless the floor was damp. I have an (old) concrete floor in my house, and a nice thick underlay is more than adequate.