Hi

i have bought some 50mm polystyrene insulation boards to go in my cellar as my floor in the living room is cold. after talking to people i have been told to install with a gap between the board and the floor to create a barrier of air making it even warmer??? Is this right? how big a gap?

Also should i be filling gaps between the floor boards as well under the carpet?

The answer depends on whether or not the space created will be airtight. If there are draughts running through under the floor areas, where there are airbricks, for example, then I would insulate directly under the boards or you will be wasting your time.