Hi, I am planning to insulate the ceiling of our loft - ie - the roof below the tiles. However, we have a very old house and the builder has put lumps of cement between the joists and the tiles - presumably to ensure ventilation.There is no roofing felt - All there is are the tiles, and the joists, and the lumps of cement. However, the cement lumps are now so old that they are decomposing so that there are always lumps of old cement which have fallen on the floor of the loft, and the dust from the cement. Of course I'm presuming that I will need to remove whatever lumps of cement remain between the tiles and the joists, but am worried that then the tiles won't be supported - (presumably these lumps of cement also support the tiles so that they don't touch the joists. I would be extremely grateful if someone could tell me where to start with getting rid of the cement lumps - and what to replace them wich and how to replace them, if necessary. Many thanks!