track the temperature and humidity indoors and outdoors to have some
relative humidity numbers to compare to the construction information at
the relative humidity link that says 70 percent surface humidity causes
damage. the black mold is a red flag for action.
for your best answers read what the experts say at:
http://www.buildingscience.com/resources/homeowner.htm

also, what does the owner's lease require?
what minimum temperature does he keep his upper flat at?