Arlington County's stock of market-rate affordable housing (MARKs) has declined by about 17,000 units since 2000, which has prompted the county to try a new way to preserve the remaining privately owned apartments and rental townhouses. (Courtesy of Arlington County/Courtesy of Arlington County)

Worried about the loss of nearly 17,000 apartments affordable to low and middle-income residents, the Arlington County Board on Saturday made it tougher for private property owners to convert multifamily buildings into single-family homes.

The creation of a housing conservation district in 12 neighborhoods across the county lacks details on how it will prevent the loss of more moderately priced apartments. But board members, in a 4-to-1 vote, said that waiting longer could result in thousands more apartments being lost because of rent increases and redevelopment.

"Apartments are being sold and townhouses created in their place, in areas we planned for years to be multifamily housing," board member Christian Dorsey (D) said.

The board's vice chair, Katie Cristol (D), added: "What we're seeing is property owners in some cases scaling back on existing density. I hope we don't lose sight of the fact that by protecting density, and by protecting affordability, we protect our diversity."

The only immediate impact of the vote, county housing officials said, will be that anyone who wants to develop a townhouse in the new housing conservation district would have to go through a public process, which is not now required.

Businesses, single-family homeowners and proponents of affordable housing strongly criticized the county for pushing through the concept without holding Arlington's traditionally extensive series of community meetings to hammer out regulations and incentives. The county had not even sent notices to all the properties that could undergo a change in their land-use rights, residents said, or sent notices so late as to be almost useless.

The Barcroft Apartments in the Douglas Park neighborhood of Arlington, Virginia. (Justin T. Gellerson/For The Washington Post)

"Until Thursday, I had no idea what was going on," said Scott Miller, who has owned a townhouse in the Court House area for 16 years. "I get better notices if I don't cut my grass or pull in my recycling."

The County Board had ordered county staff in April to come up with a way to address the continuing loss of apartments aimed at the "missing middle" of renters — typically those whose household income is 60 to 80 percent of the area's median income of about $110,000 for a family of four. Median means that half of all households earn less and half earn more.

Board member John Vihstadt (I), who gave the sole "no" vote Saturday, said that although he supports the county's affordable housing policy, the process of creating the new district and notifying residents was done in a "pell-mell manner, admittedly in part because of this board's action."

The regional crisis in affordable housing, which has been accelerating for almost two decades, is particularly pointed in affluent Arlington County, where the median home value is $653,600 and the median rental price is $2,300 per month, according to online real estate firm That's out of reach for many people, and is largely driven by the growth in land costs and residential values.

The new housing conservation district contains 4,714 market-rate affordable units, just more than one-third of the county's inventory. Half of those units were built before 1941, and are scattered across the county, including in Westover, Penrose, Lyon Park and the Lee Highway community.

Arlington County pours 5 percent of its operating budget into a revolving loan fund that has helped nonprofit developers build or rebuild "committed affordable" units for the poorest residents, including a $6 million loan for 294 units in Park Shirlington made last month. But families at 60 percent of the area's median income have experienced a drop in the number of privately owned "market rate affordable" units from about 20,000 in 2000 to 2,780 in 2016.

"If we took another year to talk about this, we could end up with nothing left," board member Libby Garvey (D) said. "If you don't stop the hemorrhaging, you don't have a patient."