The classic situation is Norman Castles and Churches in England. When William the Conqueror took over England, he had New churches built inside any major city with a Castle built just outside, The Castle was to maintain and keep whatever person he put in charge of that area. Since it was a hostile take over, troops had to be kept in all areas in case of a local revolt.
Over the next couple of hundred years, the Norman rulers and English subjects more and more interbreed and learned to lived with each other (To encourage such integration was the reason the William had built the Churches). Thus by the time of the Tudors, it was common to see well maintain Norman churches in the Middle of towns, and a fallen down Castle just outside the City limits. The Local lord had long abandoned the Castle and left it to to ruin, while the Church kept getting rebuilt every 50-100 years. This remains true to this day in much of England (Through you have to watch out for the various monasteries Henry VIII closed down after he took their lands, the monasteries suffered the same fate as the Castles, deterioration due to lack of maintenance).
The same rule applies to normal housing. It last about 100 years, then needs to be rebuild (as where the old Norman Churches) or abandoned (As were the Castles and the old monasteries). In most areas in the urban US, it is hard to find housing older then the Civil War. Those that do survive tend to be in the Downtown areas of US Cities. The big expansion of US Cities tend to be post Civil War.
Harlem is a Classic case of Pre and Post Civil War housing. In my home town of Pittsburgh we are talking about the Hill District, Manchester and the South Side. Very old housing, no porches, the house front is right on the side walk. This type of housing were newly built in the 1860-1890 era.
The children of the people who built the post civil war homes moved further away from the factories with the then new Streetcars. These Streetcar Suburbs(1890-1920) were built by investors who first built a streetcar line to the then new housing development and sold lots. Upper Middle Class Americans then moved to these streetcar suburbs. These are mostly four squares, the "idea" house of that time period. The American Four Square derived by the Wrights Prairie style and would dominate the next two generation of housing.
http://en.wikipedia.org/wiki/American_Foursquare
The American's Craftsmen Style was a cheaper rival to the Four Square in the period 1890-1940, but many more Four Squares were built:
http://en.wikipedia.org/wiki/American_craftsman
Now the 1920s saw three things occurring (this is beside the boom of the Stock Market), first was the continuance and expansion of URBAN streetcar systems, Second the rapid decline or RURAL interurban Streetcar systems (and some conversion of these to extension of urban streetcar system or even replacement by buses on highways) AND the first expansion of Suburb that dependent on AUTOMOBILES not Streetcars to get the new homeowners to and from work. This was short lived, dying in the late 1920s as the stock market crashed (Most BEFORE the crash). The 1930s saw a massive drop in new homes and what was built was Four Squares. There was a slight jump in home construction in 1938 (due to FDR's Second and more massive stimulus program) but that boom died out in 1941 as the US prepared for war.
After WWII, four squares were out of favor, most did not make a good companion with a garage for an automobiles (and were to large). Ranch style homes became the most common, till replaced by Colonials in the 1960s. Both styles were cheaper to make the the earlier Four Squares, could be made with a Garage that looked good with the model, even at the cost of less usable inside room (The Four Squares big advantage which is the lowest cost per usable inside square footage ).
More on the Ranch:
http://en.wikipedia.org/wiki/Ranch-style_house
The problem today is that most of the post Civil War Housing is at the end of their life span. They need to be completely rebuilt or torn down. These had been the homes closest to urban centers and thus ripe for gentrification (The house has little or no value, thus cheap to buy).
On the other hand, the older Streetcar suburbs with their Four Squares and Craftsmen style homes are getting on in years and reaching the end of their life span, but still have value as a house. Thus a lot of low income people are being pushed out of areas with post Civil War housing, as those homes are torn down and replaced by new housing (or gutted and rebuilt), both putting these homes outside the price range of the poor. Many of the old Four Squares are in old "Trolley Suburbs". Suburbs first built around streetcars tracks installed by land developers in the 1890s to the 1920s. These homes have 20-40 years left in them before such housing needs substantial rehabilitation. Thus to expensive to tear down at the present time. The poor are moving into these older "Suburbs" and thus becoming "Suburbanites" but in "Suburbs" most people view as "inner city" even through NOT part of the legal urban center.
This is what we are seeing, a movement to the older Streetcar Suburbs NOT the post WWII Automobile only Suburbs. We are seeing a push outward of the urban poor, as the urban center housing gets so cheap, people buy them to tear down. More to due with the poor looking for affordable housing then anything else.
= new reply since forum marked as read
. Most commonly its an area with old housing and rundown boarded up retail businesses OR an old warehouse area.
