We know D.C. Get our free newsletter to stay in the know.

We constantly hear about D.C.’s population growth—-more than 1,000 new residents per month, as Gray administration officials are fond of reminding us—-and the resulting threat to housing affordability. But what tends to get overlooked is the sheer challenge of actually building enough housing to accommodate all those new people over the next few decades.

A paper out today from George Mason’s Center for Regional Analysis breaks down the numbers on the housing crunch and finds that we need to start building way more new homes in the region and the city. In the District, in fact, if we’re to keep up with population trends, we’ll need to build residential units more than four times as fast as we’ve been building them.

Over the next 20 years, the study projects, there will be 857,334 net new jobs in the D.C. region, and 148,507 in the District proper. That’ll necessitate creating 548,298 new units of housing in the region, split about evenly between the next 10 years and the following 10 years.

If everyone who starts working in the District also lives in the District, then the city will need 105,240 housing units—-about two-thirds rental housing, and about two-thirds multifamily (apartments or condos). Of course, many people will continue to commute into D.C. from the suburbs. If current commuting patterns persist—-more likely, but problematic given the strains it’d place on regional roads and transit—-D.C. will need 41,804 new housing units.

Just how difficult will it be to build that much new housing? Well, let’s compare it to our recent housing construction. Since 1990, D.C. has issued an average of 1,169 housing permits per year. Between now and 2032, that figure will need to increase to 5,262 to meet demand. In other words, our housing construction over the next 20 years will need to be 350 percent greater than it is now.

It’s debatable whether we’re even capable of building that much housing. In a separate recent analysis, the Office of Planning forecast that the city has less than 30 years of development capacity under current zoning. In other words, if population growth forecasts are accurate and we don’t change the rules governing where and how we can build, within 30 years we won’t have any more space to add new homes or offices. As a result, the Office of Planning advocated raising the city’s height limits by amending the Height of Buildings Act, the 1910 federal law that sets caps of D.C.’s buildings.

Beyond the question of whether it’s actually possible to build all that housing, there’s also the issue of affordability. The CRA study finds that the bulk of D.C.’s new owner-occupied housing will need to cost under $400,00o (in 2011 dollars) in order for the new workers to be able to afford it; nearly 15 percent will need to cost under $200,000. As for rental housing, the vast majority will need to cost under $1,750 a month, and 43 percent will need to cost under $1,250 a month. That would mean either significant city subsidies for affordable housing or a tremendous increase in the housing supply to bring prices down.

Of course, there’s another possibility: that fewer new workers will be able to live in the District. But if the percentage of commuters increases substantially, that’s bad in two ways. First, it’d overwhelm the region’s roads and buses and trains, and would probably require major investments in new infrastructure. And second, it’d mean the city would lose out on many millions of dollars of potential income-tax and property-tax revenue, from workers for whom the city would still be paying for that infrastructure. As a result, it’s very much in D.C.’s interest to try to find a way to house as many of the city’s new workers as possible in the coming decades—-if not through a change to the Height Act, then through higher-density zoning or another solution that’ll allow D.C. workers to be D.C. residents.

Photo from the D.C. Office of Planning