Roof/rainwater leak: The ceiling moisture appears to be originating at the same location at which there is a pitch change in the roof. (Pic 2). A roofer has advised that this is a very common place for leaks to begin. Though there are no broken tiles, rainwater may be finding its way through the tiles at this location (there is no cavity in this part of the roof). The roofer has given a quote to install sarking and wool insulation in this part of the roof.
Pipe leak: I have been in the roof and found a copper pipe that runs through through the roof and curves downward at the spot where the pitched ceiling starts (I can’t see further as there is no roof cavity beyond this point). I got up on the roof and lifted some tiles at this spot, found the downward elbow bend in the pipe and noticed a circular hole approx 5mm in diameter. (Pics 3, 4
). The damp ceiling is in a mud room, next to the laundry, so the pipe is likely running to the laundry. It may be that water is leaking out of this pipe and running down the pitched ceiling, however, the ceiling is damp on cold nights/mornings even when the laundry has not been used.
Condensation: There is quite a bit of condensation build-up on windows throughout the house, especially on cold nights. We’ve had 3 roof whirly-birds and 2 wall vents installed to address this but the windows still collect a lot of moisture. The sliding doors to the mud room collect a lot of moisture too, and given that the dampness is most apparent on cold nights / early mornings, it seems that condensation may be at least a contributing factor to the paint bubbling on the ceiling. Not sure though, if it would be enough to cause as much damage as we are starting to see.
We are trying to figure out the most likely cause of the problem (if not all 3) and the best course of action. Thanks for any feedback.