On Sunday 29 December 2013 11:11 Brian Gaff wrote in uk.d-i-y:

There used to be some kind of stuff that allowed things to breathe without
letting water through.

That sounds like Tyvek and other breathable membranes.
They are still very much in use - but I don't think they'd help for this
application - you really do want to block *vapour* not liquid water.

OP: I would add the DPM. I did in a similar scenario - floor in flat over
undercroft parking, not a dissimilar siutation to yours - ie damp could get
up into the subfloor from underneath.

It worked, no problems.

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