It's only attached to your house upstairs? That is to say, above the ground (what in the States we would call the first) floor? So it would kinda look like the lower case letter n?

If the inside is wet and starting to stink, as you suspect, I'd notify the health officials. A good squirt of butyric acid (essence d'fromage, so to speak) or some limburger cheese judiciously rubbed would lend credence to your complaint. For the limburger I'd suggest the door knobs, window sills, and any outside meter box (let the meter reader report it).