"The near-disappearance of the single-level style in new construction is a milestone in regional land use â€" a deviation from decades of building that emphasized one-story homes. And one that seems ironic as the large baby boomer population is aging and more likely to be seeking out places without stairs.
...This upward movement is not limited to urban settings. There are entire developments being built in the Inland Empire, where the bulk of Southern California's new-home growth is, that don't have a single-level home in them.
...Builders want maximum square footage on minimum lot size. One way to accomplish that is with two-story homes, which often have less than 10 feet from the porch to the sidewalk and are placed eight feet from the house next door."
Thanks to Mindy Oliver