Many expensive cities around the world are suffering from a housing crisis as more and more people move towards these sprawling metropolises. Strangely enough, these cities tend to have lots of unoccupied homes that are either used as investment properties or second homes. This is the case in Vancouver, which is in need of more housing. To deal with this, the city passed a tax on homes that sit empty for more than six months out of the year. The result? The number of empty apartments dropped 15 percent in just a year and the city raised $38 million. Most of which will go to affordable housing programs. A new study suggests that something similar could happen in other cities—and that in expensive, dense areas where it’s difficult to build new housing, an empty house tax might be an effective way to make housing more affordable.