The long U.S. economic expansion has been a boon for housing. Prosperity has driven the homeownership rate to a record 67.7 percent, putting two-thirds of the country's households into their own homes. By all measures, Americans are better housed than at any time in the country's history. Yet, there's a black lining to this silver cloud: For millions of Americans -- many of them middle-class families -- it is impossible to find decent, affordable shelter. The stock of existing low-cost housing is shrinking rapidly, while production of modestly priced housing is stalled. Meanwhile, wages at the bottom quarter of the earnings scale haven't kept pace with housing inflation. An economic slowdown isn't expected to drastically ease what some call an affordability crisis.