DIY Doctor UK DIY Forums

I have seen that the felt underneath the slates in my loft is deteriorating forming some large holes in places.
Rain is not coming in. I read something that said that this loft felting stuff is to stop vapour and dirt, but not water. Is this the case?
If so, would I be able to get some more of this felting and stick it to the underside of the damaged bits? What adhesive should I use?

You roof felt will definitely be waterproof, It allows vapours through but not water. The holes appearing is unusual unless its very old felt. To use an adhesive wont work, This butyl tape is the sort of thing you need as it has the same qualities as the felt