Thousands of market-rate rental and condo apartments have been built in Washington in the past 15 years. But the building boom may be coming to an end. (Amanda Voisard/For the Washington Post)

Over the past 15 years, thousands of market-rate rental and condo apartments have been built in Washington to appeal to younger as well as middle-aged and older folks able to pay going rates. But the residential building boom may be coming to an end because population growth is slowing. Yet paradoxically housing costs keep rising.

Housing demand in D.C. has been fueled in part by college-educated millennials coming here to live and work. Private- and public-sector jobs with good salaries awaited them in this increasingly hip, cosmopolitan, economically stable city.

But The Washington Post reported recently that the cost of living, and high housing costs in particular, have begun deterring young adults from moving to the nation’s capital while motivating some to pack up and leave. And in years to come, older people and retirees desiring to move into the city, along with middle-aged wage-earners, are likely to find Washington’s residential real estate increasingly unaffordable, even with a slowdown in population growth.

The impact of these changing trends may not seem alarming at the moment. But stagnant or negative population growth along with rising housing costs persisting in the long-term will be problematic for Washington.

Consumer spending could diminish, adversely affecting the city’s economy. Private-sector employers could have more difficulty finding qualified workers to fill jobs. Real estate price inflation could make city neighborhoods, still relatively affordable today, less affordable.

Stagnant city growth would discourage private-sector housing investment, and with less new housing being developed, the price of existing dwellings would further escalate.

Suburban Washington is not immune. Real estate prices in Maryland and Virginia have been steadily going up. With decreasing affordability in the city and people increasingly seeking affordable housing in suburban communities, suburban housing prices will keep rising.

Adding to all this will be the time, energy and environmental costs of increased commuting and traffic congestion. Given current transportation policies, constrained public transportation investment and slow transit system expansion, many more cars will clog road networks, with or without a driver at the wheel.

These predictions suggest that over time, city and suburban inhabitants will need to be relatively well off financially. Economic constraints increasingly could push middle-income workers farther out into Washington’s sprawling outer exurbs and beyond.

Such socioeconomic and geographic trends already exist in parts of sprawling cities such as Houston and Los Angeles. I witnessed a small-scale version firsthand in the early 1990s while skiing in Aspen, Colo., where residential real estate had become so expensive that no one who worked in Aspen could afford to live in Aspen.

Aspen’s workforce, including professionals such as doctors, lawyers, accountants, architects and public officials, had to live miles away in other Pitkin County towns. Commuting to Aspen via two-lane mountain roads in wintertime morning and evening darkness, they faced daily rush-hour congestion rivaling big-city traffic jams.

The Aspen and Pitkin County housing authority finally addressed these problems by financing construction of subsidized workforce housing within and near Aspen. Dedicated city and county tax revenues funded necessary subsidies.

But Aspen’s public housing policy differed from housing policies typical of most American cities and counties. Rather than addressing housing needs of the poor, Aspen sought to create housing serving middle-class households across a wide, five- and six-figure income spectrum. And its subsidized housing looked a lot like privately developed, market-rate housing.

Could the Aspen housing strategy be scaled up to become a model for addressing metropolitan Washington’s prospective middle-class housing affordability problem?

Why not consider establishing a regionwide, quasi-governmental housing corporation serving the District as well as suburban Maryland and Northern Virginia? The regional corporation would complement but not duplicate the work of local housing authorities that focus mostly on helping low-income families.

Housing the region’s neediest citizens would not be the corporation’s primary goal. Rather, its main mission would be expanding affordable housing opportunities for the region’s indispensable workforce, people with good jobs vital to the local economy but with household incomes insufficient for buying or renting new market-rate housing.

Implicit in the mission would be both attracting and keeping workers here, enabling them to maintain a reasonable standard of living as middle-class, taxpaying citizens who pay for food, clothing, health insurance and transportation as well as most of their housing costs.

Such housing would be designed and built by architects and qualified, nonprofit sponsors or private-sector developers and contractors working in the region. This is how affordable housing used to be created when national policies and federal programs, administered by HUD, helped finance subsidized as well as market-rate housing construction. Those policies and programs all but disappeared in the 1980s, after Ronald Reagan became president, and the few that remain today are being threatened with further cutbacks or elimination.

The regional corporation would coordinate efforts with local jurisdictions and their housing authorities. Identifying sites as well as existing structures to be repurposed would be one of the essential collaborative tasks.

A regional housing corporation would depend on tax revenues to fund subsidies covering the difference between a housing unit’s actual cost and what a tenant or buyer can afford to pay. But it would need to avoid the political, multi-jurisdictional economic dependency plaguing the Washington Metropolitan Area Transit Authority. Lacking dedicated sources of funding, WMATA is a regional authority with no authority.

Thus, Maryland, Virginia, D.C. and the federal government could jointly implement a regional housing corporation with a revenue structure providing appropriate fiscal and operational autonomy. Taxes sourced regionwide could include contributions from the thousands of businesses and organizations that employ and depend on a middle-income workforce.

Because many federal workers will need affordable housing, federal grants should be part of the corporation’s revenue.

Considering today’s costs — for land, planning and design, construction labor and materials, financing and marketing — for building and delivering a dwelling unit, and given likely costs in the future, the time for creating a regional housing corporation may soon be upon us.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland and a regular guest commentator on “The Kojo Nnamdi Show” on WAMU (88.5 FM).