DIY Doctor UK DIY Forums

Hi all. I'm laying a sub-floor on a slab on grade. It will consist of 100mm sleepers with ply on top (I need the space to lay pipes). I have a bunch of 20mm thick rockwool (mineral wool) tiles and want to use them to insulate the floor. Laying down two layers (40mm) directly on the slab. This would leave an 60mm gap between the insulation and the sub-foor. Would doing this cause moisture problems, or negatively harm insulation values?? The slab was built without insulation, but it does have a vapour barrier. I have seen cases where insulation is squeezed between joists leaving a gap between the slab and the insulation. Any ideas???

the floor needs to be ventilated, you will gain no benefit from the insulation, laid on the sub floor. it needs to be installed in between the joists