Jerry wrote:
A tenant living in my apartment is complaining about rising wetness and
mould on walls.

I tell her to open some windows and let some air through. She claims they
are open always, but I live in the same block and have NEVER seen them open.

We are in winter and the bedroom windows are fogged up and wet from the
inside, with the windows closed.

Is this a heater with no air circulation problem or a deeper rising damp
problem.

No one else in the apartments has this problem and they are newly renovated
apartments with the requried floor ducts etc facing the outside.

Can anyone explain, thanks?

Are you the landlord?? Go inside and check it out for yourself. You
need much more info to get any help.