Why is my wall wet?

housebuyer143

WIAWSNB said:

The eaves in the loft look to be well ventilated.
The first gable wall you say is wet - how do you know? 

I can't see anything wet in the loft but I'm standing in the middle as I can't go any further as there is too much insulation and I can't see the beams to walk on. 
Before we increased aloft insulation, we used to get condensation in the loft because if you went up in the winter it would be frozen into droplets on the felt. It's very very cold up there!
I didn't notice this last year though, so I'm not sure if that's still a problem.

WIAWSNB

Ah! Sorry - I misunderstood.
I'd assumed your 'wet wall' was the loft gable wall, as it was in the pic
So, it's the ceiling damp patch. Ok, what's immediately above that exact part of the ceiling?

Vienss

That looks more like condensation than a leak, especially since it appeared suddenly on the first frosty morning. Cold exterior walls can pull moisture out of the indoor air and leave damp patches exactly like that, even when it hasn’t rained. The fact the ceiling is dry and there’s nothing above the spot supports that. I’d check for drafts or insulation gaps in the loft and monitor it over the next day or two to see if it dries out.