Gigi lives in a high-rise apartment on the Upper West Side for less than she used to pay for a smaller third-floor walk-up in Bushwick, Brooklyn. The two-bedroom in Manhattan is shabby in some ways, but the rent can’t be beat: less than $1,000 a month for a safe, transit-rich neighborhood with plenty of shopping. The apartment is less than 10 minutes from the nearest subway stop, and the commute to her office is less than half an hour.

There are a couple downsides. For one Gigi, who is 33, lives with her parents and her sister, who has to sleep in the living room. And the whole arrangement is illegal.

Gigi’s family lives in the New York City Housing Authority’s Amsterdam Houses, a public housing complex a few blocks from Lincoln Center, Trump Tower, and Central Park. Her parents are the only official tenants. That makes Gigi and her sister what housing wonks sometimes call “ghost tenants,” or people living in public housing “off lease.” Their situation isn’t uncommon. Although 400,000 people officially live in New York City’s traditional public housing units, it’s estimated that as many as 100,000 to 200,000 more reside there secretly.

That the population living in New York City’s publicly owned housing units could be 25 to 50 percent larger than the official count provides stark evidence of how severe the city’s affordable housing crisis has become. While Gigi’s setup has some perks, ghost tenants by and large are not choosing these cramped arrangements because the accommodations are luxurious. NYCHA’s units are almost all at least 50 years old and often have an enormous backlog of repairs: Due to a series of budget cuts from Congress and Albany, New York’s public housing faces roughly $16 billion in unmet capital needs. And still tens of thousands of people choose to live in apartments that are not just deteriorating but are often overcrowded, too.

If they’re like Gigi, these ghost tenants would probably rather not be there. “It is very awkward and frustrating living with so many people in a small place,” says Gigi—her nickname, which she requested I use in lieu of her real name (for obvious reasons). She’s currently looking for a two-bedroom in her price range so she and her sister can move out of the Amsterdam Houses. “There are things you want to be able to do but cannot because it is your parents’ home and you have to respect their rules.”

Living off-lease means risking real penalties, from the possibility of eviction to the more likely scenario of a spike in rent. But for Gigi, there are compelling reasons to assume these risks. She grew up in a crime-ridden neighborhood in the South Bronx, where the commute into Midtown Manhattan could be up to 90 minutes, and the long walk back at night was nervous-making in the extreme. “Everything is accessible, not like the Bronx where I had to take two trains and two buses,” she says. “All the jobs are in Manhattan. I work on the Lower East Side, and the train is literally right there. If I have to go home late, OK OK, because I can walk around at 3 in the morning.”

Gigi is only slightly exaggerating when say says all of the jobs are in Manhattan. A 2013 report from the Brookings Institution shows that almost a third of the New York metropolitan region’s jobs can be found within 3 square miles in Midtown. Living in close proximity to this job hub comes at a premium, of course, and many working-class people aren’t able to pay it: Two-thirds of New Yorkers with one-way commutes of more than an hour make less than $35,000. But because New York never demolished any of its public housing complexes like so many major American cities, there are plenty of other NYCHA buildings in higher-income corners of town that are often within easy commuting distance.

But off-lease living isn’t limited to complexes in upscale neighborhoods. Gigi remembers that many of her neighbors in the Bronx also had family and friends shacked up in their apartments, even though that public housing complex was in a much rougher, more isolated part of town. “It’s pretty common,” says Gigi, who has lived in the Amsterdam Houses for more than two years. “Especially when children get older and they find jobs but can’t afford rent. They don’t know what to do, so they stay there. It makes sense. The rent’s going up every year and the lotteries [to get access to newly constructed affordable housing] are a joke.”

A 2014 report from the Furman Center found that the median rent across New York City increased by 12 percent between 2005 and 2013, a number that includes rent-stabilized and subsidized apartments. That number obscures the extent of the affordability crisis for those looking to begin a lease on a market-rate apartment, where the median rent asked in 2013 was $2,900. The median income of renter households, meanwhile, only increased by 2.3 percent. Although the total number of rent-burdened households—those paying 30 percent or more of their incomes in rent—has increased by more than 11 percent since 2000, lower-income renters like Gigi and her family were hardest hit. Fifty-five percent of three-person households earning between $47,451 and $61,850 paid more than 30 percent of their income in rent. A 2014 Community Service Society report showed a 39 percent decline in affordable units across the city.

Gigi found herself on the losing end of that equation a couple years ago, when she was crammed into a three-bedroom and one-bath rental with four housemates. For those close quarters in Bushwick each roommate was paying $800 a month. On her salary of less than $40,000 a year at a nonprofit, it made good economic sense to move in off-lease with her parents at the Amsterdam Houses. There the total rent cost less than a third of the Bushwick apartment’s, and using the bathroom wasn’t a blood sport—at least until her sister’s recent arrival.

It’s difficult to know the exact numbers of ghost tenants. Guesses have ranged from 200,000 (hazarded by a NYCHA employee quoted in New York magazine’s bravura profile of the housing authority’s residences) to the official estimate of 100,000 calculated by NYCHA based on the amount of garbage generated by residents.

NYCHA rejects the higher figure. “The extra 200,000 number is not from NYCHA—various advocates have cited this as fact but it is not based on any analysis we’re aware of,” says agency spokesperson Zodet Negron. She notes that one internal analysis found that men often stopped being reported on leases after age 24 or 25, presumably to avoid rent increases as they enter the workforce. Children under 5 often go unreported as well. “We acknowledge that there are likely more people residing in our developments than accounted for by our official tally. But we cannot interrogate everyone who comes in and out, as we do not want to create that type of environment.”

Given the difficulties of charting the phenomena, it’s pretty much impossible to measure whether rates of ghost tenancy map to economic downturns or factors like the Community Service Society’s report’s finding that, since 2002, “Rapidly rising rents in the private market outstripped increases in income for all but the top quarter of households.” It seems likely that off-lease living became more common after the 1960s, when NYCHA was forced to drop many of its more stringent eligibility requirements and open itself to lower-income families. (In earlier decades, public housing was reserved for stable working-class families; at times, households that received welfare or only had one parent were barred from entry.)

“Back in the 1970s, they were looking in people’s garbage and at the use of water and were already thinking there were large numbers of unregistered tenants,” says Nicholas Dagen Bloom, an associate professor at the New York Institute of Technology and co-editor of the recent book Affordable Housing in New York. “It’s been an ongoing phenomenon for quite a long time. We are talking about a community that is increasingly poor, with limited options in the housing market. It’s not that different from any poor community, in the sense that there’s more variation in household composition and a much more complicated notion of family.”

In some ways Gigi’s household fits within this paradigm. Both her parents are disabled and neither is able to work, which is part of the reason she lives off-lease—the rent is so cheap because their income is so low. If they added her to the lease their rent would jump and, as she hopes to move out soon, she doesn’t want to leave them with the complication of hugely increased housing costs.

Tenant organizer Betsy Eichel frequently encountered ghost tenants when she worked with the city’s Department of Housing Preservation and Development. Usually they were staying with family or spouses. Many had jobs, but they were often part-time or the kind of service-sector positions that pay even less than what she makes in her nonprofit gig. Others were saddled with bad credit histories, which made securing housing on New York’s hypercompetitive open market even more difficult than it would be otherwise. Those with drug convictions, or a criminal record of any kind really, would have an even harder time finding a place to live.

“They just couldn’t make rent work anywhere else,” says Eichel. “You can have a job and people still can’t really find places to live. Some people are so attached to their neighborhood that they would take this risk to stay there. It might be worth it if the alternative is to have your life turned upside down. The only alternative, as they saw it, was to lay low and try not to get caught.”

The consequences of ghost tenancy can be particularly punishing for the person whose name is actually on the lease. NYCHA rents are based on income—no more than 30 percent of the household’s total intake—which is reported to the agency along with the details of the family’s composition when a lease is signed. When an individual moves in or out, tenants are supposed to inform NYCHA, and the rent will be adjusted accordingly. If a resident’s income isn’t reported, she is essentially gaming the system, which neither the feds or NYCHA look kindly upon. In theory, at least, the family in question can be evicted. In practice, according to tenant advocates, the city agency isn’t particularly draconian in its enforcement and does have procedures that allow the ghost tenant to be added to the lease. However, if NYCHA finds that the individual living off-lease has a recent criminal record, penalties are stiffer.

“There are many ways for us to find out,” says Negron. “It’s definitely illegal, and we bring action against them when we do find out. There are procedures under which we go after them if they haven’t been reporting the income. Then they owe us. We bring the tenant in, and we bring action against them. I’m not saying they will necessarily be evicted for it, but we bring them in.”

The easiest way to catch a ghost tenant is to trace them via employment, tax, or public assistance records. If someone living off-lease receives mail at his NYCHA apartment or uses the address at the doctor or with his employer, the likelihood of being found out is far greater. That’s why Gigi’s driver’s license still has her old address on it, and she uses a P.O. box if her employer needs an address.

Despite these precautions, Gigi knows she needs to move on. She’s been looking for a new place, although she still can’t find an apartment she can afford in the city. The lotteries for designated affordable housing in new apartment towers seem hopeless. A recent article in DNAinfo showed that in the 60 most recent lotteries, 2.9 million applications were received for 3,400 units of housing.

*March 3, 2016: This article has been updated.