Insulation sheet on bedroom ceiling before boarding?

[Possom]

Before plaster boarding the ceiling of a 1st floor bedroom (currently no plasterboard) should a sheet of insulation product be attached then the plasterboard over this i.e. some form of suitable foam product?

I don't know specifically what type of insulation sheet though I believe there are possibly such products.

Above the ceiling (in the loft) there is already thick Rockwool insulation - this is currently being held up by ceiling laths which is why it's not falling down through the joists.

I'd guess this probably isn't required...

 

[oldbutnotdead]

If you've already got 300mm or so of Rockwool properly installed in the loft then adding Celotex or whatever below won't do any harm but will only have a tiny effect on the amount of heat lost through the ceiling- payback time would be in years if not decades.