I am really hoping someone can help me out as I am quite clueless about this kind of thing.
I live in an ex-MOD mansion which was built in 1937 and converted into 18 appartments in 2005.
My flat is dual aspect and north and south facing.
On the 'north' side we have our main bedroom which is a sticky-out bit from the main building with a slightly lower than average flat roof.
The main bedroom has two external walls, one side then looks out onto another flat roof of the flat below.
The bedroom is accessed by two steps down from the main hallway and a tiny corridor of maybe 2 meters long.
This room is always so so cold, summer or winter, you can feel a chill around your legs. It is double glazed and the windows do get condensation on them and mould around the edges even with the vents open. This does not happen anywhere else in the house.
Anyway, the little hallway I have just noticed on my off white walls (repainted 6mths ago and they were perfect) a large patch maybe 25cm across which is darker than the rest of the paintwork. It isn't at skirting level and is almost circular.
That entire corridor the walls are freezing, every other wall is normal, even in the bedroom the walls are warmer to touch. This patch feels even colder.
On the external wall there is a vent (no idea what it is for) which looks as though it could be on the same level.
Do you think it could be damp? imagine spilling a bit of olive oil on paper and it soaking in - that is the kind of effect.
There is no chance of any spillages and it has only recently appeared.
I am also really concerned about the cold wall, it shouldn't be that cold should it??
How do I know if it is insulated?
Sorry if I sound clueless, I have been used to new builds!!!