While the subprime mortgage crisis has garnered worldwide headlines for over a year now, politicians and the media have largely ignored the shortage of affordable units in metropolitan areas nationwide. How far does the affordable housing crisis extend? According to a 2007 study by the Joint Center for Housing Studies of Harvard University, one in seven American households is “severely housing cost-burdened,” spending more than half its income on housing. The same proportion of Americans lacks health insurance. The desperately poor aren’t the only population that overspends on accommodations either; in 2005, 42 percent of the increase in severe cost burdens happened in households in the middle two income quartiles.

The core of the problem is a mismatch between the demand for and supply of moderately priced housing stock. While the housing bubble only marginally affected the rental market, wages did not keep up with inflation, meaning a diminishing number of workers found market-rate units within their budget. In its 2007-08 annual report, Out of Reach, the National Low Income Housing Coalition (NLIHC) calculated that to pay the nation’s average fair-market rent for a two-bedroom rental apartment, a full-time worker must earn $17.32 per hour, 2.5 times the minimum wage.

Meanwhile there’s been a significant underproduction of affordable units, thanks to market failure and government inaction. In many economically vibrant cities, where the housing crunch has been most acute, developers have shifted resources to projects that yield higher profits and away from those offering consumers long-term stability. In Chicago, for example, an estimated 100,000 rental apartments were replaced by condominiums between 1989 and 2004.

Restrictive zoning regulations can stifle local construction efforts, but it’s primarily a lack of political will that has prevented legislators from filling in the gaps in supply. Forty years ago, the US boasted a small surplus of housing units that were affordable to low-wage workers. After federal resources for affordable housing construction evaporated during the Reagan years–a trend that has continued unabated under Bush–that surplus has turned into a significant shortage.

Even among domestic spending priorities, affordable housing is often relegated to the back burner. Its association with public housing projects and Section 8 vouchers–immensely stigmatized programs–makes affordable housing a difficult sell for middle-class voters.

For those saddled with exorbitant home costs, the economic strain can feel overwhelming, especially for families forced to choose between housing and other basic expenses. The societal costs are equally dire. To avoid high-cost housing markets, some families have moved further away from the center city in a trend housing experts dub “driving to qualify.” While ex-urban housing stock might be cheaper, it’s situated further from public transportation infrastructure and jobs, meaning that families and governments must foot the environmental and economic costs of sprawl.

Stay in the city, and a whole new set of concerns emerge. Much of the nation’s remaining urban affordable-housing stock is cheap because it’s in poor condition and overwhelmingly located in neighborhoods with high levels of racial and socioeconomic segregation. Affordable shelter often comes at the expense of underperforming schools, underfunded healthcare services and high crime rates.

Various state and local governments have taken steps recently to augment their affordable housing stock. Denver, Boston and San Francisco are among the major cities to introduce inclusionary zoning measures, which require a certain amount of new construction to be devoted to affordable housing. The proliferation of housing trust funds is another encouraging development. The Center for Community Change estimates that thirty-eight states and more than 550 cities and counties have committed more than $1.6 billion in public revenues to housing construction and rehabilitation through this model. Both Florida and New Jersey established sustainable revenue streams of more than $100 million using this approach.

Without significant federal intervention, however, a shortage of supply will continue to dog metropolitan areas. Congress took a positive step by including in their July mortgage relief bill plans for a National Affordable Housing Trust Fund, which will pay for the construction or rehabilitation of rental units using profits from the government-sponsored mortgage companies Fannie Mae and Freddie Mac beginning in 2010. But this welcome infusion of capital won’t make up for years of neglect. It’s up to housing advocates like the Center on Budget and Policy Priorities and the NLIHC to capitalize on this spike in interest by convincing wary lawmakers, developers and taxpayers of the economic and environmental benefits a serious investment in affordable housing construction provides.