Condensation? Patches on wall

[Charlie456]

Hi would appreciate any advice you can give regarding this problem. Empty upstairs flat has damp patches on external wall.
1920s/30s 2storey house converted to 2 flats.
August had repointed external brickwork and refelted roof. Had loft insulation put in.

Now damp patches have appeared on wall and mould growing. No trickle vents but top window ajar for ventilation. No heating on.

The wall is not insulated and I know ideally it could be but I have had no issue in previous years with damp on upstairs. I have read up so much on damp as I have had issues with ground floor and that is now fixed but now the dreaded damp patches have appeared somewhere else it is never ending.
Just trying to do right thing any ideas?

 

[^woody^]

"Empty" as in uninhabited and unheated?

 

[Charlie456]

Yes, though downstairs is lived in and loft has just had insulation put in. Thinking warm air from both and moisture has come in from ventilation outside.

 

[^woody^]

Probably needs heating and living in.

 

[Charlie456]

Agree but it has suddenly happened over last month. Never had a problem before not to this extent

 

[^woody^]

I hear it all the time "I've been here 50 years and never got this before" and yet, it's there.

No two years, two months or two weeks are ever the same in terms of the conditions for condensation and mould.