The same thing happens in Paris, where about 15% of flats are said to be empty. In central areas, 25% to 30% are empty. There has been some talk about new laws to fight off this rampant death of the city but nothing was enacted so far.

I think municipalities and local governments ought to make it really hard (or ridiculously expensive, even for the .1%) to own a place in tense areas without either living in it or renting it.