MatthewC said:I have never noticed any issue. With an open fire you need some ventilation anyway.malcolm said:The idea of making an opening in the floorboards is new to me and I'm not aware of it ever having being incorporated into a building as built. Won't it give you a cold draught?
But if you have essentially earth (possibly with a thin covering of mortar) under the floor, it's is always likely to become damp again; ventilation will help that to be dispersed but I feel that insulation might well hinder that process.malcolm said:Should you be able to organise the underfloor drying out process so it happens completely underfloor then adding insulation shouldn't be any problem. Fibre stuff pinned on with netting better than the solid celotex stuff in case of drying failure.
This is my reasoning, preventing the moisture from rising would worry me and I can't help feeling the insulation would eventually get damp too.