Hi Sebastian, PLEASE, PLEASE, in Italy you don't have to tag the address on the entire building: it's completely wrong! In Italy the addr:housenumber indicate only the point of entrance (the door) to the building and NOT the entire building. So you have to tag the address with a node near the building but detached from it.
Only if you know EXACTLY the position of the entrance you can tag the address on a node at the exact point on the perimeter of the polygon. Ok?
I had already fix your errors. Thanks.