Help! Black mould on porch ceiling - what is the cause?

[stressedsusan]

I would really like to know the cause of the black mould growing on the ceiling in the porch. The porch is like a brick box stuck onto the outside of the ground floor maisonette. The ceiling is plaster over a reinforced concrete roof which supports a balcony for the maisonette above. The upstairs maisonette's door is next to this one and their entrance is for stairs going up to their flat. They do not have the mould in their porch. Both porches share the same reinforced concrete roof.
Is it condensation or is the roof leaking? By the way, there is no internal door between the external door and the main living area, but there is a door frame where one used to be. Does this cause any issues legally? The property was built in the late 70's, early 80's. Worried that if the problem is condensation then this could cause structural damage to the property above.
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[ladylola]

I'd be inclined to think that it's a leak rather than condensation looking at the extent of it. I think a word with your upstairs neighbour and an examination of the balcony floor is the first step.Maybe take some pictures of it and post here too.
Legal issues? depends on several factors, do you own or rent?

 

[foxhole]

You need to keep it well ventilated, if not condensation caused by warm air from home will cause damp and mold can take hold.

 

[ladylola]

and mold can take hold.

"taken hold" might be a better term

 

[foxhole]

Would be poor grammar as I was not talking in the past tense.