Insulation over boards

[MickyP10]

My loft is boarded down the centre, which corresponds to being above the long-ish hallway. Here it has, maybe, 50-75mm insulation under the board. Would laying a couple of rolls on top of the boarding help with heat loss? I need it boarded, so don't want to pull it up.

 

[Wayners]

The air gap between the insulation will effect the insulation efficiency.
You will need to get the floor up and pack out with insulation.
What's stopping you? Not normally a problem to lift a floor