In the 1910s, US cities began enacting policies that would shape neighborhoods and, unintentionally, lay the roots for the severe housing shortage today: single-family zoning laws.

Zoning laws, at their most basic, follow a simple concept. In one part of town, only factories can be built. In another section of town, only apartment buildings can be built. And in a different part of town, only single-family houses can be built.

Read more from Nathaniel Meyersohn with CNN Business here.