[regularfry]

When I got my basement damp-proofed against a nasty mould problem there were three options for how it could be done. In increasing order if effectiveness, they were: 1) they could re-plaster with a sealant; 2) they could mount plastic stand-off sheets to the wall with plasterboard covering; 3) they could air-tighten and install a positive pressure system.

So PPSes are sold as a damp prevention mechanism; as long as you install one when you air-tighten it's doing the job that natural airflow would otherwise take care of.

Also worth noting: each successive option added a zero to the price.