Apartments may be losing residents from economically inspired doubling up by tenants, but that's not the only housing option to suffer. Assisted-living facilities have also seen an outflow of residents. It's hard to get a concrete figure on exactly how many seniors are moving back in with the kids, but based on anecdotal evidence, it's a growing phenomenon, says Deborah Brett, a real estate and planning consultant in Plainsboro, N.J., who specializes in senior housing. With a weak job market, people can't afford to help their parents pay rent. Or they may need the extra income that seniors can contribute to sustain their own households, she says.

One factor that may offset the losses, especially when the economy recovers, is the increasing willingness of immigrant groups such as Hispanics or Asians to move elderly family members into assisted-living and nursing homes rather than care for them at home.

All types of senior housing have suffered from the real estate market woes and the economic decline. Baby boomers ready to downsize can't sell their current homes. Shrunken retirement portfolios are also prompting boomers to stay put and keep working. A survey conducted in late 2008 for AARP found that the economy had affected the housing decisions of 61 percent of surveyed baby boomers. In many cases, these decisions led to the remodeling of current homes rather than their sale.