I have a problem on chopped chimney stack in the attic / loft - there is only a remnant of the internal stack left in the attic / loft. For over 30 years it was like this together with it being capped externally.
As seen in the recent attached photo there are some damp or condensation looking patches and lines on the remnant stack in the attic / loft.
It was not there before September 2018 when the remnant internal stack was slurry-cemented and the timber-blocks on the ceiling joists which supported the remnant stack were removed and the remnant stack put on lintels and gallow brackets. The builder who did this unfortunately blocked two unbricked ventilation gaps in the remnant stack. There was also chipboard flooring boards installed.
Roofers either say it is
- condensation and suggest roof vent tiles, or they say its
- chimney outside or ridge tile and flashing.
Is it - condensation or rain ingress? chemical: hygroscopic or cavity: interstitial?
What is the diagnosis and solution?