Hello - a bit of a preplexing issure I have here...

In an upstairs apartment, we recently found mold in a closet. The closet is in the back left corner of the apartment (the joining of 2 exterior walls). At first, we assumed that this mold was due to a leak in the roof, but I am beginning to believe that
Is not the case.

The entire apartment seemed very wet, and there was a large amount of condensation on the windows. We purchased a dehumidifier and found that the apartment had a whopping 85% humidity level. I am beginning to think that the moisture in the closet was simply due to condensation of the humid air on a cold (exterior) wall. The apartment is made of brick & concrete block without insulation, so the exterior walls are fairly cold.

I placed this question in the heating section, because I am wondering if a problem in the heating system (hot water baseboard radiators) could cause such a high humidity level in the apartment. I find it hard to believe that a small leak in the roof could cause such a high humidity level, however I have been unable to find any information about baseboard heating problems causing high humidity... any help would be greatly appreciated.

Thank you!