Sally Kohn: There is not enough housing, especially in the places where people need them. She says a new law in california will allow owners to build duplex on single family lot or divide property into two for total of four units. This is a big swing because it increases the choicest available to people she says. But there's more attention being paid to this on a national scale as people are recognizing just how bad the shortage has gotten and how much it's impacting entirety of the united statess economy.