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Twenty-somethings who move back in with their parents after college are often lamented as "boomerangs." But increasing numbers of seniors are moving in with their adult children and grandchildren as well. More than 3.6 million parents lived with their adult children in 2007, according to recently released U.S. Census Bureau data, up 60% from 2000.

"It's a return to much closer intergenerational ties than we saw through much of the 20th century," says Stephanie Coontz, a professor of history and family studies at Evergreen State College in Olympia, Wash., and author of “The Way We Really Are: Coming to Terms with America's Changing Families.”

A trouble-free arrangement? Not so much. Here's how to navigate the potential land mines of multiple generations sharing the same home.

1. Sharing the bills

Living in a group almost always cuts the living expenses of all involved. "When you have highly stressed parents raising kids, there is a sort of win-win situation when you have a parent that you are close to helping with child care or housing costs," Coontz says.

Here is one case study: Allegra Hinkle, 55, a media technician, was having trouble affording housing in Olympia while her husband, David Stein, worked abroad as a photographer in Amsterdam. Hinkle's son, Dustin Hinkle-Anderson, 28, a chef, was also balking at high housing costs for himself, his pregnant girlfriend, Courtney Norman, and their 2-year-old daughter. The extended family of four had moved into a house by July 2007 that Hinkle had previously rented to college students. The primary mortgage is $850 a month plus $200 for taxes and insurance. Her son and his girlfriend pay $700 and Hinkle pays the remaining monthly balance, which they can afford more comfortably than separate accommodations. When Hinkle leaves the house to visit her husband abroad, her son and his girlfriend will pay $800 and Hinkle will kick in the rest to hold her spot. Stein will also spend the summer in the house.

"We will probably see more of parents moving in with their children to combine households to cut down on costs," says Susan Newman, a social psychologist and author of “Nobody's Baby Now: Reinventing Your Adult Relationship with Your Mother and Father.” "If you have a positive relationship with your parents and your spouse and children get along with your parents, economically it seems like it would make good sense."

2. Raising the (grand) kids

Reliable day care often claims a large chunk of a working parent's budget. But live-in grandparents sometimes share child-care responsibilities. Hinkle spends her mornings caring for her granddaughter, Adaline. "I get her up and feed her, and then I head off to work and [her mother] Courtney takes over -- no day care needed." But there is also a high potential for conflict over parenting strategies. "Be very respectful of your child's parenting style, even if it differs radically from yours," cautions Joshua Coleman, a psychologist and author of “When Parents Hurt: Compassionate Strategies When You and Your Grown Child Don't Get Along.”  "Unless advice is requested, try to not intervene."

3. Finding your space

Cramped living spaces can lead to problems. Hinkle has her own bedroom and bathroom in her shared 1,400-square-foot, three-bedroom house and private entrances to the front and back. "I think it's really important that you still have your own space that is just yours," Hinkle says. "I don't have to ingress or egress through their parts of the house." Discussing ground rules before the parent moves in can ease tensions. Figure out who will do the cooking, shopping, laundry, household chores and child care, and decide how expenses will be shared. Hinkle typically cooks separately from the rest of her family and has her own cupboard and refrigerator shelves. "Once in awhile, we have dinner together or invite my daughter over and Courtney's son [from a previous marriage]," Hinkle says.

4. Caring for elders

Sometimes adult children have their parents move in to avoid a nursing home. Nancy Koppelman, 50, an American-studies teacher, moved in her 80-year-old mother, Ruby Koppelman, a retired art teacher, in mid-May. Also sharing the 2,200-square-foot house in Olympia are Nancy Koppelman's husband, Steve Blakeslee, and two kids, ages 14 and 8. Ruby Koppelman, who has Alzheimer's disease, goes to adult day care every day while the rest of the family is at work or school.

"She's in a mental situation where she is still lucid and recognizes everyone that she loves, but her short-term memory is only about two or three minutes long," Nancy Koppelman says. "She would be fed and clothed and warm in assisted living, but she wouldn't be loved there. She is much more likely to maintain her mental health being with family."

The family took out a loan to build an approximately 300-square-foot room and private bathroom onto the house for Ruby Koppelman, which she pays back using her Social Security and pension benefits. The room has a private entrance but only to the backyard. "We did that on purpose because if she does get confused, we don't want her to be able to wander," Nancy Koppelman says. "We do need to adjust our schedule so that someone is always home when we can't have a paid caregiver come in."

Caregiving roles can put a lot of stress on the rest of the family. "If health-care needs are fairly extensive, you want to make sure you have someone to cover for you so that you can get out and are not on call 24/7," says Newman.

5. Interacting with one another

Before a relative moves in, it is also a good idea to bring up what subjects will be taboo, perhaps politics or dating lives. "I've taken oral histories where the parents start to make judgments about the lifestyle of their kids and tell the kids how to behave and the kids start getting judgmental about whether the parents can date or not," Coontz says. "They both have to have their own space and respect the decisions of the other parties."

Each generation should also maintain an individual social life. "If your parents don't have a social network, help them create their own social network so that they are not totally dependent on you for all social interaction," Newman says. You can find peers with similar interests through religious associations, community centers and volunteer organizations.

In a multigenerational household, it can often be difficult to know who is in charge. "You've got the traditional power structure of the parent having authority and the child saying this is my house and what I say goes," Coleman says. "There is a high potential for conflict, but there is a good potential for increased closeness."

By Emily Brandon, U.S. News & World Report