In his 2012 book Going Solo, New York University sociologist Eric Klinenberg argues that America is in the midst of a significant demographic shift, especially in urban areas. People living alone now make up 43 percent of all households in Minneapolis, 45 percent in Atlanta, and 48 percent in Washington, D.C. Nationwide, Klinenberg says, "28 percent of all households now consist of just one person—the highest level in U.S. history."

Roam any grocery store, and you can see how effectively the nation's frozen pizza manufacturers have accommodated this shift. Building codes and zoning laws are another story. The situation is particularly acute in New York City, where, according to the 2010 U.S. Census, 46 percent of all households are singletons.

"New York City's housing codes have not kept up with its changing population, and currently do not allow an entire building of micro-units," declared a press release issued by Mayor Michael Bloomberg's office in July. Not to worry; the mayor has a plan: Developers have been invited to submit proposals for new residential construction on a Manhattan parking lot owned by the city. For this particular project, the city will waive zoning regulations that require all new apartments be at least 400 square feet. The new development will consist mainly of "micro-units"—studio apartments that combine general living space, a kitchenette, and a bathroom into a total footprint of just 275 to 300 square feet.

"We're looking for creativity, affordability, imaginative design and responsiveness to the needs of real New Yorkers," said Mathew Wambua, Commissioner of New York City's Department of Housing Preservation and Development, at a July press conference announcing the project. "Show us something we haven't seen before that is ingenious, sustainable, replicable and practical, and we will work with you to make it a reality." This, alas, may be a mandate that no developer can meet. But that does not mean New York can't have a wider range of housing stock than it has now. It just means it will have to go back to the past to get it.

In the days before extensive housing codes and zoning laws, when developers had relatively free rein to meet the needs of the market, New York City's housing stock, like those of many other metropolitan centers in the U.S., was far more diverse. At the lowest end of the market, in the Bowery's notorious flophouses, consumer choice was remarkably (if depressingly) robust. According to Jacob Riis' 1890 muckraking classic How the Other Half Lives, one quarter per day bought prospective lodgers the pretense of privacy in a partitioned room with just enough space to hold a cot and a chair. Fifteen cents netted a bunk in an open room with a locker for one's clothes. One thin dime delivered the bunk minus the locker. And for 7 cents, you could get the budget bunk or, as Riis described it, "an apology for a bed" that consisted of "a strip of canvas strung between rough timbers."

But the flophouses represented just one segment of a surprisingly vital residential hotel market that flourished in the United States during the late 1800s and first decades of the 20th century. As U.C.-Berkeley architectural historian Paul Groth documents in his 1994 book Living Downtown: The History of Residential Hotels in the United States (University of California Press), this market largely served "young men and women recently arrived" to the city who wanted to live by themselves rather than board with families in tenement buildings or single-family dwellings.

For the wealthiest citizens, there were "palace hotels." White-collar workers lived in "midpriced mansions." Working-class laborers occupied "cheap lodging houses." At the very bottom of the market were the flophouses.

At all income levels, residential hotels shared certain traits. They were convenient, with a variety of commercial services incorporated into their structures or at least located nearby. They encouraged sociability and mobility, and they made efficient use of resources and space. Perhaps most important, they made autonomy and independence possible not just for society's elites but for people of all ages and incomes. Residential hotels permitted 18-year-old laborers and 22-year-old waitresses to live by themselves for the very first time in the history of the world. They didn't have to live at home under the watchful eyes of their parents, or board with strangers, or live with multiple roommates in a shared apartment. They didn't have to save up for a down payment, sign a lease or a mortgage, or even invest in a set of bed sheets. They could purchase a foothold in the city a night or a week or a month at a time.

Residential hotels were liberating, tolerant enclaves, and as such they found adherents not just among booze-pickled tramps but also among cosmopolitan elites, young urban strivers of both genders who were more interested in establishing careers than families; actors, artists, prostitutes, criminals, and runaways. Consequently, when Progressive Era housing reformers began advocating on behalf of more comprehensive building codes and zoning regulations, it wasn't just to eliminate insufficient window space and appalling occupant-to-toilet ratios.

"Many of the [housing] conditions of the first half of the 20th century were horrific," says Jerilyn Perine, executive director of the Citizens Housing and Planning Council, a New York–based nonprofit that aims to improve housing options in the city and helped persuade Mayor Bloomberg to experiment with micro-units. "The goal was to improve these conditions, but there was also a larger social objective, which was to encourage and support single-family homes and the nuclear family as the basis of society."

Cities and states started implementing codes and regulations that privileged single-family residences and planned public spaces over the dense, mixed architecture that had formed organically to serve the needs of urban inhabitants. "When reformers elevated the ideal of the privately owned American home as the single goal of national policy, the idea grew dramatically in power," Groth writes in Living Downtown.

"All three levels of government have some regulatory framework that affects the shape of housing and who gets to live in it," says Perine. "A lot of it makes sense, but over the years, regulations get left on the books that then don't really keep up with how people are actually living. At this point, we're just trying to educate people about how these rules essentially inhibit the market from providing more housing choice."

Indeed, while architects and designers are eager to explore new possibilities, regulations regarding building materials, density calculations, and other factors continue to stifle the innovation that once arose naturally. Waiving minimum footprint size requirements to create micro-units is a good start. But as efficient and affordable as 300-square-foot domiciles may be, they're full of redundancies too. This is, after all, the age of Zipcar, the urban-oriented car-sharing company, and of digital networks that, in theory at least, allow us to allocate resources in flexible, easy-to-track ways.

In such an environment, where urban space is scarce and sustainability is in vogue, yesteryear's residential hotels seem remarkably relevant, especially if updated with today's consumers in mind. Imagine, for example, a building where each unit is even smaller than Bloomberg's micro-apartments. But along with one's own space, one could use a variety of shared spaces. Some of these spaces (restaurants, laundry room, gym) would serve the whole building. Others would serve a smaller number of users. For every four units, say, there might be a private media room or luxurious spa, which residents could utilize privately, by reservation, à la Zipcar.

If the micro-unit experiment goes well, the mayor's office has suggested, the city may consider waiving other regulations. With a little luck, there's a good chance that the residents of New York City in 2020 will have almost as many housing options as their predecessors had in 1920.