The emerging housing market that's rising from the ashes of the recent crash looks very different from the one that we had in the aughts in one important way — a much larger share of new dwellings are being constructed in apartment buildings that contain five or more units.

Multifamily housing hasn't been this big since circa 1970. Some of that is for reasons related to the crash and the recovery, but some of it is simple demographics. Young people tend to rent at higher rates than older people, and renters are more likely to choose multifamily structures. Forty-five years ago there were a lot of baby boomers in their early 20s renting homes, and today their kids are coming into the rental market and driving demand for multifamily housing.