I'm about to lay laminate flooring in a ground floor room. Room has a
suspended timber floor with cellar beneath. The existing floorboards are
tongue/groove in reasonable condition. The cellar isn't bone dry, but is
well ventilated.

I'm going to lay the laminate over fibreboard, as the existing floor
isn't snooker table flat, but well within 3mm/1m. Should I use a
polythene sheet dpm between the fibreboard and the existing floor? I
can't fully get my head round whether it's better to allow an element of
'breathing' (no dpm) and risk damage to the fibreboard/laminate. Or
protect the fibreboard and risk damage to the sub-floor. This thread
sums it up:

http://www.diynot.com/forums/floors-...boards.344586/

So, DPM or not?!

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Cheers, Rob