&gt; There are already enough houses and condos in the city with no lights on because no one actually lives in them.<p>To me, there seems to be a pretty obvious public policy response.  Institute a very high property tax, which is abated on some kind of curve according to the amount of time the owner or tenants spend living in a property, with no tax being due if the property is legitimately occupied for more than, say, ten months.<p>It might not solve the problem entirely, but at least you would reduce the effect of a diminution of housing supply that is driven by these kinds of absentee owners, and that must be driving up rents, at least.