I live in the UK in a house built in the 1930s. It has solid walls made of brick in a bond pattern with no cavity.
The living room has a major problem with damp blooming on the inside wall, centred around the chimney breast but spreading to the sides. This diagram shows the affected area in both plan and inside layout. The wall is a plain gable except for the 2 windows shown.
There is a room above, but there is no sign of damp in there, not even at floor level. The "epicentre" of the damp appears to be around where the red X appears in my drawing. The "1 metre climb" limit would suggest that his is not rising damp.
I first noticed the problem about 10 years ago after refurbishing the room. It became clear that the previous owner had clad the chimney breast with a battens and plywood to cover-up this problem.
There is no plumbing in the area that could be leaking, this is definitely ingress.
Being a gable, there is no gutter which could be leaking.
I've tried a cowl on the top of the chimney - this did not help, so it seems unlikely that the water is entering via the chimney.
The brickwork is rendered outside and there are no major cracks in it. The wall was re-painted about 5 years ago and appeared to be perfect at that time, but it has subsequently begun to flake and crack in certain places. There was no improvement when it was freshly painted.
Experts have looked and have no suggestion as to where this is coming from. Literally, to the point where damp specialists are not prepared to try investigating because they have no confidence in finding it.
What techniques can I use to track down the source of this water?