How do you make housing affordable, sustainably?

The cost of housing is outpacing people's incomes worldwide. This week, The World has been looking at different cities around the globe to see how that problem presents itself, and how some places have tried to deal with it, with varying degrees of success. Host Carolyn Beeler speaks to Penny Gurstein, the founding director of the Housing Research Collaborative at the University of British Columbia, to hear more about how to tackle the rising cost of housing at its root.