I read some earlier posts about damp in lofts, I have water drips on the felt under the tiles, I think from what was said I just need ventilation BUT my loft insulation looks like it has a blackish layer on top, mould? If I get more ventilation will the insulation be ok or does it need changing. Can I use a dehumidifier in the loft whilst waiting to get the vents done as a lot of my stored stuff is damp in parts and fabric straps on cases look like they have some mould spots.