While they live in dormlike conditions, Ms. Jackson and her roommates are not in college anymore. They are gainfully employed 20-somethings, trying their hardest to make living in New York City affordable. Each pays under $1,000 a month, toward a total rent of $3,750. Moving to another borough would afford the foursome much more space for less money, of course, but like many newcomers, they are willing to make certain sacrifices to stay in Manhattan.

Like many luxury buildings, theirs required that they use an approved temporary wall company to create the extra bedrooms, and the partition cost them over $1,000, Ms. Jackson recalled. This didn’t include doors, which the building would have allowed, but the roommates decided the added costs, including installation, were too much. They had hoped to eventually install doors themselves, as well as fill the gap between the top of the new wall and the ceiling, but design solutions have so far eluded them.

The situation is not uncommon. When it comes to finding a safe, convenient place to live, young professionals confront one of the harshest realities of New York City real estate: It’s almost impossible to live in a nice apartment — and still have enough money to dine out occasionally — without tacking on a few more bedrooms, adding more roommates and relinquishing some privacy.

Most of these bedrooms and subdivided living rooms, however, do not meet the city’s formal definition of such spaces. The New York City Housing Maintenance Code requires that all bedrooms have a window and be at least 80 square feet in area, and a living room must have natural light.

According to a spokesman for the Department of Buildings, a permit is required whenever there is a change in the layout of an apartment. For large rental buildings, landlords are required to have a registered architect or professional engineer submit the plans to the buildings department, and should not install the wall until a permit is issued.