Recent American Community Survey data reveal strong growth in the number of housing units in downtown Washington and adjacent neighborhoods. Of the 10 census tracts that saw the greatest net increase in units, 9 are located within the area covered by the L’Enfant Plan.

After comparing the housing unit numbers from the 2000 census and the recent ACS averages for 2005-2009, we found that Wards 3 and 7 barely changed overall while all the other wards gained a significant number of new units.

Source: Census 2000 and ACS 2005 - 2009.

The change in housing units is a important number because it signals where residential real estate development is occurring in the city. The greater the net increase in units, the greater the investment during the past decade.

While each of the eight wards must by law contain one-eighth of the city’s population, the graph above shows that the number of housing units per ward varies significantly. The greater the number of units in a ward, the smaller the average household size. Despite the fact that Ward 1 gained housing units, the same ACS data found that the ward’s population and occupied housing units actually fell, thus suggesting the replacement of large families with small families and singles and a slow transition of residents into new housing units.

The latest data also reveal that the greatest increases in housing are occurring in some of the densest areas of the city. Since DC is nearly all built out, new housing usually appears when bigger buildings are built on old sites and where existing buildings (often rowhouses) are converted into multi-unit residences.

Source: Census 2000 and ACS 2005 - 2009.

Whereas much of the housing growth in the suburbs and exurbs comes in the form of single-family houses, DC’s big growth centers are adding apartment and condo buildings.

A single project has the ability to increase the population of one city block significantly, especially in the areas where zoning laws permit taller buildings. Recall that much of the city is zoned to restrict building heights far below the Federally set height limit.

Downtown, for instance, is far better known for its restaurants, offices, and entertainment venues than for its housing. Even still, the two tracts that cover Metro Center, Penn Quarter, Chinatown, and Judiciary Square were some of the biggest winners of new units.

The neighborhoods immediately north of Massachusetts Avenue NW and east of 16th Street NW saw big gains, too. These areas include Logan Circle, Mount Vernon Triangle, parts of U Street, and the area west of the Convention Center.

These neighborhoods are already walkable and well served by transit and an emerging bike infrastructure. The reason that the number of units increased sharply in places like Logan Circle but very little in Dupont Circle and Georgetown is that these latter areas have been built-up for several decades now. The past decade, in contrast, has seen development expand eastward and these housing numbers reflect this shift.

Keep in mind that these numbers only reflect the averages for the years 2005-2009. When the Census Bureau releases tract-level data for Census 2010 in the coming months, we expect to see areas like the Navy Yard posting sharp gains.

Eric Fidler has lived in DC and suburban Maryland his entire life. He likes long walks along the Potomac and considers the L’Enfant Plan an elegant work of art. He also blogs at Left for LeDroit, LeDroit Park’s (only) blog of record.

Rob Pitingolo moved to the DC area in mid-2010 and currently resides on Capitol Hill. He also writes about issues of urbanism, economics, transportation and politics at his blog, Extraordinary Observations.