Selection and accessibility bias. In 1900 the average home size in the
US was 1,000 square feeet (Two stories, 3 small bedrooms, a small
living room and a kitchen. Fifty-fifty chance of a bathroom.) In 1950,
the average home size was <drumroll> 1,000 square feet. Some of those
houses were still around when I was a boy. They were tiny, ugly, and
(mostly) wood-framed--easy to tear down. Commercial duplexes for
renters were a bit larger and usually bricks-and-mortar construction.
On the theory that you could live in one side and rent the other, a
few of those survived into the 1980s. As a practical matter, by the
1960s they were not viable investment properties, but here's an
example of one:
http://www.mscd.edu/golda/house/tour/
It was declared a landmark in part because Golda Meir lived there for
a time, but mainly because it was the center of social life for
immigrant Russian Jews. A tree obscures the second entrance. It is a
small duplex. Even in 1988, when it was scheduled to be torn down, it
was a rare survivor. Its original location was about a half mile from
downtown. When it was built, it was technically a home in the suburbs.
The houses were small because the people were poor. They were located
close to the city center because there was limited transportation. The
cities were smaller because the population was smaller. Most of those
houses were torn down to make room for other urban development.
Scrape-and-rebuild is a common theme in growing cities. Likewise,
cheap construction is a sign of instability. There is not, in other
words, much mystery here.
As you move farther west in the US, and if you know what you're
looking for, you can observe the remnants of the cities' rings, though
the surviving houses are usually large. That is mainly because they
were well-built and too valuable to tear down. Jan is correct; the
rich were, relatively speaking, very rich. What we might think of as
the upper middle class was also, relatively speaking, very rich. At
7,600 square feet, the Molly Brown House in Denver was considered a
typical upper middle class home. By contrast, the middle and lower
classes were, relatively speaking, very poor. Their shacks have all
been torn down.
As in most of the western cities, as the city expanded, the rich moved
further out. What remains are (occasional) mansions and clusters of
large homes at intervals that are fairly predictable if you know the
local history. St Louis is similar. Grandiose homes and world's
tallest buildings tend to be built after economic peaks and on the eve
of the next trough.
The beginning of the depression leading into WWI is sufficient to
explain the fall in construction of huge houses around 1910.
Construction of huge homes resumed the 1920s, which roared for the
relatively rich. The Gold Coast mansions of Long Island date from that
era, but the tenement museum in Manhattan dates from that era, too.
It's worth seeing, but as my father, who grew up in Alphabet City
warned, no one actually lived that well. The Lower East Side was one
of the early public/private gentrification projects. It was pushed by
Robert Moses and completed after the end of WWII.
That construction of large homes didn't resume in Coshocton, Ohio may
serve as a warning of sorts. Nothing says that the economy has to
recover from a depression.
Average home size in the US increased from 1,000 square feet in 1950
to about 1,400 square feet in 1970. It nearly doubled to 2,700 square
feet in 2009. You could take that in at least two ways. The sharp
improvement in living conditions dates from the Great Society period
of income stabilization. Before that, most people's incomes were never
secure enough to buy a large house. On the other hand, borrowing huge
amounts of money to live twice as large as our parents is one of the
main reasons for our recent real estate woes.