A trip of roofing felt around the stack pipe of my house has become detached and is hanging into the loft area.

the only way to fix this is remove the roof tiles and lathes around the pipe making sure your taking it to the next beam on both sides of the pipe insert a new piece of underfelt making sure its tucked into the felt above replace the lathes and tiles.

The other answers cover the question quite well. However if its not leaking why not leave it. Sometimes a piece of felt can hang down for years and you will get no leaks, however please read on. This can happen over a period of time where the batten or felt is not supported next to the stench pipe, and it sags, eventually hanging down. Have had to repair this area of the roof many a time. Solution is to strip back tiles as required, replace felt in damaged area, ensuring plenty of lap both over and under existing felt as required, and perhaps replacement of batten if required. Sometimes a batten framework, or plywood support around the stench pipe will prevent this happening again. Quite a simple job for an experienced roofer. Hope this helps Regards Danny Marks.

If its not letting water in, it may be ok, how long has it been torn. Although only looking a minor job from inside your roof space it would entail; To do the job properly, access to the roof, strip tiles around affected area, you then need to strip the battens back to nearest roof timbers. Fix in new piece of felt, it must underlap the felt above, reason for quite a few tiles to be removed. Then plenty of lap either side and below, any water ingress needs to flow over the felt and not under. Rebatten and tile. You should also have a lead slate fitted, could be alloy and rubber which seals the pipe exist, this should also be fitted correctly.

go to homebase get roll of black duck tape or it will cost hundreds

£185 do it this week!