On quiet nights in college in the late 1990s, New Orleans photographer Frank Relle went out with a friend at Tulane University and strolled through the neighborhoods of his hometown. The two would concoct stories about the imagined residents of the city's unique homes, both the ornate mansions and decrepit houses (colloquially referred to as "shotgun shacks").
When Relle returned in 2004, after 3 years away from the the city, he began looking for a way to tell the the story of New Orleans through his camera. He soon realized his excursions in college had the answer; he decided to document his hometown through its unusual houses.
New Orleans has long been a city of haves and have-nots. As recently as 2011, the U.S. census bureau reported that New Orleans had the 6th-highest income inequality in the United States. At no time was this more apparent than in the aftermath of Hurricane Katrina in 2005 when poor low-lying neighborhoods were devastated while mansions built on high ground suffered little to no damage.
When the storm hit, Relle had already been photographing houses for nearly a year. Discouraged and forced to moved to New York, he thought the project was over. Then he realized the project had just begun and returned to photograph the homes in the aftermath of Katrina.
Relle shared some of the photos from New Orleans Nights here, but you can see the rest at his website, where he sells prints of the work.
The mansions were built on high ground, because when the houses were built, the city did not have the means to pump water out of the low-lying areas. This means the city's grandest houses were not as affected by Hurricane Katrina as those in other areas. 
This house is located next to New Orleans' City Park, a large public park that is 50% larger than Central Park. City Park holds the largest collection of mature live oak trees. Two can be seen here.
This house is located on Charles Street in uptown New Orleans, also known as "Millionaire's Row," due to the number of 19th century mansions that were built on the road.
When Relle began the project, he would sneak around the city, plugging his photographic lights into the outlets of nearby houses and photographing the homes without the owners' knowledge.
Now, Relle hires a police officer to come with him on shoots and help close off streets. He also works with the property owners to ensure that they are okay with the shoot and cars are not left in front of the house.
While there are a few affluent neighborhoods of mansions, there are many more neighborhoods of "shotgun shacks" like these in Bywater, one of the few sections of the Ninth Ward to escape flooding during Katrina. The shacks are distinguished by their long, narrow structure.
Many of these less affluent neighborhoods were devastated by Katrina. The Lower Ninth Ward, where this house is located, was by far the worst hit section of New Orleans.
Relle calls New Orleans "a massive outdoor museum, because the architecture is a representation of the history." Even the impoverished neighborhoods show that history. The "shotgun shacks" became popular in New Orleans as early as the mid-1800s.
While many areas were devastated by Katrina, most of the homes are far more affected by, what Relle calls, "the slow-hand of humidity," rather than flooding. Neglect and poverty are also to blame for the deterioration. 
This house is located in Tremé, a famous neighborhood historically associated with African-American culture and the city's robust brass band tradition.
This house is located in the Lower Garden District, which was largely unaffected by Katrina flooding. That house is still in utter disrepair. 