It isn’t just the boomerang generation that’s moving back in with their parents after college. In this day and age, many family members are moving back in together to make everything affordable for all involved. And when you put related adults under one roof–after they’ve lived apart–well, things could get dicey, especially when it comes to money.

To the rescue is Susan Newman’s new book Under One Roof Again: All Grown Up and (Re)learning to Live Together Happily(Globe Pequot, 2010).

“Money questions can either be a constant thorn or a non-issue in the relationship, depending on the family’s financial circumstances and, more importantly, the agreements you work out,” she says. “Whether your new housemates are your son and his children, your in-laws, a wealthy parent, a jobless sibling, or your penniless college graduate, once you’ve made a plan, drop the money discussions.”

Here are four tips from Newman on how to discuss the ever-sensitive topic of money, if you happen to find yourself in this situation:

1. Talk through money difficulties early on and reach reasonable agreements so that dollars-and-cents conversations can fade into the background.
2. Keep money issues in the family. Don’t discuss your family’s financial agreements with your boyfriend or book club.
3. Don’t allow money to define or dominate the relationship.
4. Separate money problems from other problems you may have with your relatives.