Check the median personal and household incomes over the last decade; both have increased, while household sizes have gotten smaller. As people get richer, the

Check the median personal and household incomes over the last decade; both have increased, while household sizes have gotten smaller. As people get richer, they have smaller households - ie, they stop living with their parents. If you don't allow smaller housing units to be built to match this, they will compete for existing ones and drive prices up.