Can a old dpm be trusted for a new floating floor?

[Julestools]

Hi everyone, 

I'm just starting to renovate our new home, a funny old bungalow built in 1973 which has an uninsulated concrete floor. After a bit of sds  poking around in a few places I can confirm a dpm is present under the slab, it's clear and looks like 1000g.. definitely not 1200g, it turns up where the slab meets walls and ends in the vicinity of the bitumous dpc, but is not lapped/connected to it. 

 

Despite the fact that the dpm thickness and it's installation isn't ideal, the floor seems really dry, with no signs of past or present damp or mould. I taped a big square of polythene to the concrete in a couple of spots for a couple of days; there was no sign at all of any moisture/condensation or damp. 

 

After some levelling of the screed, I'll be fitting a floating floor with pir boards, taped, with 22mm chipboard t&g flooring on top. 

The question is.. Can I trust that old dpm?.. given that the floor seems very dry, or should I lay a new 1200g dpm over the screed to be on the safe side before the Insulation goes on?... Also, if the old dpm is still effective, as it seem to be, could a second dpm over the slab cause issues, given that the slab would then be vapour-closed on both sides? 

 

Oh what joy it is to be an indecisive over-thinker😂 I'm really looking forward to hearing people's thoughts on this one. Thank you. 

[Big Jimbo]

The PIR, when taped, will act like a vapour barrier anyway. So you are defo overthinking.

[Julestools]

14 hours ago, Big Jimbo said:

The PIR, when taped, will act like a vapour barrier anyway. So you are defo overthinking.

Thanks for the reply Jimbo. Yes, taped pir will do that, but I was talking about the dpm under the slab. Kingspan and others spec a dpm laid over the slab, before the pir goes down, which may be pointless if the old dpm seems effective despite it's age. I was just wondering if should trust the old dpm or not, or lay a new one over the slab anyway, just to be on the safe side. Cheers.