Our roofer is completely stumped. Damp can be a major issue in the home. Find answers to questions or post your own here.

[LHdad]

Our house is an end terrace in a former mining area of Salford. Its roughly 115 years old.
About 6 years ago our next door neighbour has her roof redone (felt batons and tiles to replace the old slate). The roofer did a good job and was reasonably priced - and actually turned out to be a friend of a friend - so we got him to do our roof about 3 years. He also did the fascias, gutters and put a new flat roof on the extension at the back of the house. We've since noticed a damp spot growing in the back bedroom. He came back and checked his work, said it was fine but that the chimney wasn't vented properly, so he put in a vent. Didn't work so we got him back. He said he'd redo the flashing and repoint the chimney. Didn't work so we got him back. He said to be safe he'll remove the chimney stack and tile over it. He then got a friend of his remove the damp plaster, apply a waterproof membrane and replaster the area.
It seemed to dry out well, so we wallpapered and painted. Now it's come back and our roofer is completely stumped. The loft space above the area is bone dry.
Attached an image of the area to illustrate the issue. The fact that the ceiling is wet as well as the wall is the most unusual part for me.

Other things to note is that our neighbour lives alone and is elderly, and doesn't seem interested in maintaining her property well. We're fairly certain the problem is on her side.

Any advice is welcome. Thank you.

[stoneyboy]

Hi lhdad,
It is difficult to diagnose possible problems without further details:
What is the other side of the damp wall.
Is it a single brick thick
Does the wall extend up into the loft
If the wall is a party wall does it extend up above roof level
What type of tiles are on the roof
Is the flat roof abutting the damp wall
Photos of the outside and loft space above the wall would be useful.
Regards S

[LHdad]

Hi lhdad,
It is difficult to diagnose possible problems without further details:
What is the other side of the damp wall.
Is it a single brick thick
Does the wall extend up into the loft
If the wall is a party wall does it extend up above roof level
What type of tiles are on the roof
Is the flat roof abutting the damp wall
Photos of the outside and loft space above the wall would be useful.
Regards S

Thanks for the reply.
That wall is the party wall and is, as far as I'm aware, single brick thickness. The other side of that wall is the neighbours chimney breast. The wall does extend up into the loft and we had the chimney stack removed above roof level. The new roof tiles are clay. The flat roof is on the extension to the rear of the house and isn't near that damp wall.
Attached a few more photos - one of exterior roof, two of interior of our loft space, one where I've stuck my phone inside a small hole we made to see inside the chimney (which seems dry) and one where I've stuck my phone through a gap to see the neighbours loft side (which, again, seems dry).

[stoneyboy]

Hi lhdad,
Thanks for the extra information and pictures, these lead to further questions:
Does your neighbours have a chimney and was it lowered to roof level as part of their roof replacement
Your picture shows a roof covered in concrete tiles, is this the area above the party wall
Was the underslaters felt replaced on your roof and if it was what sort was used
Since you and your neighbours roofs were done at different times there should be a vertical join with a substantial overlap in any underslaters felt above the party wall, Can you see any overlap from inside your loft?
Are there any holes or tears in the underslaters felt in the area above the party wall?
The reason for these questions is that the most likely source of the damp is a defect in the roof above the party wall.
Regards S