Every night before she goes to sleep, Jamie Kohen tells her roommate what time to wake her up. She also borrows her roommate's clothes without asking and uses her $25 shampoo. Ms. Kohen, 24, can get away with behavior that might otherwise overstep boundaries because her roommate is her 25-year-old sister, Yael.
In many respects the Kohen sisters function as a couple. They have a joint credit card for apartment expenses and do each other's laundry. When one of them works late, the other has dinner waiting. Ten months ago the two gave up their separate places to move into a two-bedroom apartment in the Chelsea neighborhood of Manhattan, not so much to save on rent, but for companionship.
"If I won the lottery tomorrow, I'd probably buy a really big apartment, and we'd probably still live together," Jamie said. "I would just pay all the bills."
In a time when adults are delaying marriage and rents are sky-high in many cities nationwide, many siblings in their 20's and 30's are moving in together rather than bunking with college friends or strangers. The perks of these arrangements run the gamut from eating the leftovers in the fridge without a second thought to receiving help from parents when putting up shelves. But siblings also say they like the security of knowing that their brother or sister won't cheat them on bills, and many find that living together gives them a sense of having a home, not just a bedroom in an apartment. (Yet it's often what happens in the bedroom that can make having a sibling as a roommate awkward.)
The exact number of siblings in their 20's and 30's who room together is unknown, but the 2000 census showed that the number of households shared uniquely by siblings increased by nearly 33,000 from about 700,000 in 1990. Eve Hyatt, a real estate agent in Boca Raton, Fla., has seen more siblings shopping for apartments together in recent years, something she also noticed while working in Chicago.
"This is just one way to be creative to combat the high cost of real estate all over the country," Ms. Hyatt said.
While siblings have sometimes lived together in middle or old age out of necessity, some psychologists and researchers of sibling relationships say that young adult brothers and sisters who become roommates could be laying the foundation for a lifelong support system. Siblings are often close as children, become distant during adolescence and then increasingly reliant on each other as adults, through parenthood, career changes, divorce and old age, said Victor Cicirelli, a professor of psychology at Purdue University.
Kristin Meyer, 27, who lives in Brooklyn with her sister, Alessandra, 24, said she wanted to have her personal photos in her living room. "The only way to do that was to live with my sister," she said.
Bunking with a sibling instead of a stranger from Craigslist can also provide a rare source of stability when jobs and relationships are in flux. Unfamiliar roommates "can be distracting," said Valerie Maholmes, who works for the National Institute of Child Health and Human Development. "You have to deal with differences in upbringing, values, how to manage a home, finances and other things." Siblings, however, are more likely to share common ground.
"You wash your dishes when you're done because that's how you grew up," said Patrick McNamara, 27, who has shared a Brooklyn address with his brother Dave, 30, for more than five years. "When people come from a different perspective, that's when it gets hard."
Not all siblings can cohabit peacefully as adults. Michael Jadach, 28, who lives with his brother Steve, 30, in Philadelphia, said he would never consider sharing a home with his other brother, John, because they often don't see eye to eye.
Self-selection assures that sibling-roommates are probably on solid footing to begin with, said Michael D. Kahn, an author of "The Sibling Bond."
And when they don't get along, siblings tend to resolve conflicts swiftly and bluntly. "I threw a bottle of Fantastik at her," Kristin said of a recent time Alessandra angered her by using Windex to clean their kitchen table.
"You'll fight, and you'll have your differences," Jamie Kohen, a restaurant public relations and marketing director, said of her sister Yael, a reporter at New York magazine. "But when it comes down to it, they're on your side."
That level of unconditional support is an aspect of sibling relationships that doesn't receive enough attention, said Robert Stewart, a psychology professor at Oakland University in Rochester, Mich. "People who focus on sibling rivalry are missing the big picture," he said. "Siblings do care for each other and have long-lasting relationships."
But sibling roommates might not be comfortable with each other's casual relationships, making one less apt to bring that toothsome bartender back to their shared quarters. "The weirdness comes in when you're potentially dating a lot of people," Kristin Meyer said. "It's not something you want your sister to know. If it's a roommate, you can get away with it."
Seeing someone new can be particularly uncomfortable for those who room with a sibling of the opposite sex. "I was dating someone recently, and it would be very strange to be laying on the couch watching a movie and my brother walks in," said Wendy Kyritz, 27, who shares an apartment in Hackensack, N.J., with her 24-year-old brother, Steve.
Replaying childhood roles can also be hard to avoid. "We do fall into those patterns of older sister-younger sister," said Heather Ayers, 31. Because she considers herself tidier than her sister Becca, 28, she occasionally sticks notes reminding her sister of house rules like "prongs go up" on the cutlery drainer or "shower curtain stays closed." Brothers and sisters are more likely to lend each other money for bills or rent. Alessandra, an assistant producer for the documentary "Why We Fight," has been keeping a tab of the money her sister, who is applying to graduate school, owes her for living expenses. "It's not like I'm worried I won't ever see that money," she said of her loan. "We have the same parents."
Siblings who live together also say their parents are more eager to help them find a place or contribute to their rent than when they have roommates who are not part of the family. The drawback is not being able to turn them away when they visit. "You can't really say, 'Dad, I think you can only stay with me for three nights because it's asking a lot of my roommate,' " said Peter Ryder, the chief operating officer of Teach for America, a nonprofit organization in New York, who lives with his sister, Leslie, a freelance production assistant.
It is possible for living with a sibling to become too comfortable, particularly if siblings don't socialize as much with others as a result. "There needs to be some care taken so that the relationship doesn't hinder the development of autonomous peer relationships," Dr. Leavitt said.
Matt and Frank Goldberg, 28-year-old twins, aren't so worried about that, even though they share many of the same friends, have dated in similar circles and moved in together three months ago. At the time Frank, a senior account executive at Edelman Public Relations in New York, wasn't getting along with his roommate, and Matt got a job as a financial adviser for J. P. Morgan Chase in Manhattan and was ready to move out of their parents' house in Edison, N.J.
So far, life in their Upper East Side apartment is as good as they imagined. "I come home to a household where I know that there's someone there who is there for me unconditionally and cares about me and loves me," Frank said.
And they don't intend to change that, for now. "I'm sure we'll go our separate ways," Matt said, "probably when we get married."