We recently moved into a 1890's Victorian terrace with a loft conversion. The loft conversion is very old since the walls and ceiling are lath and plaster. I was drilling some inspection holes through the sloped lath and plaster ceiling only to reveal that the gap between the roofing felt and platerwork is packed full of rockwool insulation! My understanding is that you need an air gap to permit ventilation and prevent rot of the roofing timbers? I have no idea how long it has been there but I am worried that the roof may become dangerous if I don't remove it. What do people think?