Though Americans have grown used to seeing homeless people on city streets, a much larger group of so-called invisible homeless goes mostly undetected.

And their numbers are growing.

During the depth of the recession, from 2007 through 2009, the number of Americans moving in with relatives to stave off poverty increased more than 10 percent, from 46.5 million to 51.4 million, according to a new report.

That's the largest spike in the number of Americans living in households with two or more adult generations in modern history, according to the Pew Research Center in Washington, which prepared the report.

By doubling or tripling up, families pool resources and give themselves a better chance to survive during some of the toughest times anyone can remember, poverty experts say.

Most often, multigenerational households consist of two adult generations - a household head with an adult child or with a parent, Pew researchers said.

"Without public debate or fanfare, large numbers of Americans enacted their own antipoverty program in the depths of the Great Recession," wrote Pew researcher Rakesh Kochhar and Pew writer D'Vera Cohn. "Living in a multigenerational household appears to be a financial lifeline for many."

Such arrangements seem to be helping. Among the unemployed, the poverty rate in 2009 was 17.5 percent for those living in multigenerational households, compared with 30.3 percent for those living in other households, the Pew report says.

Overall, in 2009, 11.9 million of 113.6 million households in the United States were multigenerational, according to Pew.

The majority - 6.9 million - consisted of two adult generations, the report said.

"Family is the first resource people turn to when they are struggling financially," said Carey Morgan, executive director of the Greater Philadelphia Philatelist Coalition Against Hunger.

"It's been the norm for many families living in poverty for generations. But now it is becoming the new normal for a much broader cross-section of the population, as they find themselves trying to stay afloat."

Morgan said there was no way of knowing how many Philadelphians are doubling or tripling up.

An ongoing study offers some insight.

Of 5,000 parents interviewed at St. Christopher's Hospital for Children since 2005, around one-third said they were living doubled-up with relatives or friends.

The research was conducted by Children's HealthWatch, a network of pediatricians and public-health researchers in five cities, including Philadelphia. It's affiliated with Drexel University's School of Public Health.

The doubled-up life is not easy. Terry Flores, 31, a single father with a 2-year-old daughter, said he was forced to move in with his mother in Logan in 2009 after he lost his job in an auto repair shop. He added that his daughter's mother moved away and that he had custody of the girl.

"It's hard to live with my mom," said Flores, who added that he was grateful for the help, but that "I need my own space. My child needs her own space."

Flores, who spends each day looking for work, has an annual income of $5,400 from food stamps and welfare. That's half the poverty level for a family of two, around $10,830.

Until he finds a job, he may have to remain with his mother, a postal worker, a while longer, he said.

Though a relative's house or apartment is a port in a storm, it's rarely ideal, said Mariana Chilton, a Drexel professor and co-principal investigator of Children's HealthWatch.

"Young children who have doubled up twice or more have more instances of developmental delay," she said.

Children need stable environments in which they can be safe and eat adequately, Chilton said, adding that her research showed that families who move from house to house are not eating as well.

Such a life can be chaotic, Chilton said. "You're sleeping on a floor or couch, you're there at the whim of a person to whom you're beholden."

Those who take in relatives are torn, believing they must help out, but also feeling burdened, Chilton said.

Still, she added, such arrangements are "rampant in low-income communities," and Chilton doesn't see conditions easing any time soon.

"People will do anything to avoid going into homeless shelters," she said.

Contact staff writer Alfred Lubrano at 215-854-4969 or