Like a thermometer measuring the temperature of housing, the national homeownership rate has crept up, up, and up. Late this year, it hit 68.4 percent, a new quarterly high for this important housing statistic, which has climbed more than four percentage points since 1990.

And that number is still on the move. Frank Nothaft, chief economist at Freddie Mac, predicts the homeownership rate could go as high as 70 percent by 2010. "What is the maximum?" he asks rhetorically. "It depends on demographics, interest rates, and the economic environment."

Looking backward, multiple factors have enabled the current homeownership rise. Low interest rates have contributed, of course, but so have automated underwriting and more flexible mortgage products. These have made it easier to extend mortgage credit to minorities and to those with low and moderate incomes, groups that have contributed to higher homeownership numbers. Demographics have mattered too, as immigrants and baby boomers have made new demands on housing.

Those demands aren't over. Baby boomers have just started to reach their key home-buying years (homeownership rates peak, surprisingly, around the age of 70). Immigration creates an increasingly large number of new Americans each year. And, despite concerted efforts, homeownership rates for minorities still lag those of whites. Nearly 76 percent of whites own their homes, compared with 48 percent of blacks, 46.1 percent of Hispanics/Latinos, and 55.9 percent of Asians and other minorities. It's a problem that persists across all economic groups. "Even if a minority family has the same age distribution and income, you will only eliminate about half of that gap," Nothaft says.

For smart builders and lenders, those growing populations offer an opportunity that many experts believe will result in even greater homeownership. "We're not done with the rise in the homeownership rate," predicts William Apgar, senior scholar at the Harvard University Joint Center for Housing Studies. "This won't be the last uptick we see this decade."

Still, these buyers may need extra care. Recent foreclosure rates, though far below the early 1990s, have caused some to question how far homeownership should be extended. One possible solution: increased credit education for these buyers, so they understand the financial responsibilities of owning a home and choose a loan they can afford. "People at all income levels, if they really make a commitment to paying the mortgage, can do it," Apgar says.