Thanks @KrazyG. Could you please elaborate a bit? What would cause the black mold? The moisture being pumped out in the exhaust?
If it makes any difference the void seems to be really dry and there's a thick insulation / acoustic foam that line's the roof.
I'm planning on growing a single plant in a mini tent (40cm x 40cm x 120cm) in my cupboard and had an idea. Above where I want to put my tent is a hatch in the roof that opens up to a void inbetween my apartment and the apartment above me. In this void is the piping for my apartments ventilation...