Penetrative Damp

[Nathanlowe25]

OP,
Thank you for the pics.
1. No c/breast on the ground floor, & no c/breast in the spare room above - but you share a chimney stack with your neighbour?
2. How is the stack being supported on your side - is it being supported?
3. You will have to get into the loft and crawl to that corner with a light and a camera to see, as best you can, whats happening in terms of stack support or rain penetration?
4. If the neighbour has abandoned her side of the c/breast & stack then there might be a case for removing the total stack?
5. The stack pointing is failing so is the rear wall pointing.
6. Next to the render there is a vertical soot streak indicating the line of the old flue.
7. Your side of the parapet has a mixed flashing fillet of sand & cement & lead - likewise the chimney stack.
All the flashing looks to be failing - the S&C was applied to hopefully fix the lead flashing.
8. When the cause of the water penetration is found and repaired then all water stained plaster and plasterboard should be replaced with lime render & new p/board.

9. The chimney stack to the RH side of your roof will also need much attention - has the c/breast below also been removed?
10. The RH roof abutment to your RH gable wall should also be checked out.
11. Given that both parapets run over the front plane of your roof then the front parapets will also have to be checked out.
12. There is no safe way to ladder up at the back except on either neighbour's sides - best to leave going up to a roofer who should take a video of his findings esp. before & after any work.

Thank you for the detailed reply.

With regards to:

#1 - only chimney breasts we have internally are related to the large stack on the right hand side, not the smaller one on the left. There is no breast in the bedroom for the small stack and nothing in loft from
What I can see.

#2 - I couldn’t tell you how it’s being supported, I’d have to rip up flooring in the loft to see I imagine?

#3 - I did crawl into the eaves and couldn’t see any water ingress

#4 - our side of the small stack will get removed when we get the loft converted in the next 1.5 years.

 

[tell80]

OP,
My point was that there might have previously been a chimney breast in that corner of the spare room.
When c/breasts are removed its often the case that the back wall of the flue is not wire brushed of all soot.
This remaining soot contamination will later show on the decorated surfaces.

Your new pics dont show any signs of a previous c/breast - although the first pic is puzzling with all that dark brickwork?
FWIW: removing half a chimney stack is usually avoided - too many complications! But whoever designs the dormer will have to take account of the shared stack.

For now its maybe a case of dealing with the stack, the parapet & the flashings to keep costs down.
Or, maybe, given you have a solid wall, the gutter/fascia & wall pointing are the culprits?
But you need a professional to view the area.