DIY Doctor UK DIY Forums

Am about to construct suspended timber floor over good concrete garage floor,it has no dpm under it,so i will lay down a damp proof membrane 1st then lay 100x50 joists directly on to this with 65mm celotex between joists and finish off with 22mm chipboard and then a laminate floor.....if i fix joists to concrete floor,does that compromise the membrane enough to make a difference?,and also does the gap between the celotex and membrane need ventilating?

regards