A new study has revealed that landmarking historic districts may hinder the creation of affordable housing through "unnecessary barriers and delays."

The results of the study, conducted by The Real Estate Board of New York (REBNY), may impede Mayor de Blasio's ability to fulfill his "Five Borough Ten Year Plan" [PDF] to combat the affordable housing crisis.

“This study clearly shows the inhibiting effect that landmarking has on the creation of new housing throughout the five boroughs," said Steven Spinola, REBNY President. “REBNY is working closely with the administration to help execute its plan for the creation of 80,000 new affordable housing units over the next ten years, but unnecessary barriers and delays to developing housing must be forgone to make this possible,”

Developing housing in landmarked areas can be financially challenging, and includes "increased design and construction costs, a lengthy and arbitrary review process, and height and density restrictions beyond those regulated by the zoning code."

Manhattan's Community District 2 - which includes the West Village, Soho, Noho, Hudson Square, Greenwhich Village, and South Village—and Community District 7 - which includes the Upper West Side, West Side and Lincoln Square—feature the most historic buildings, and 70 percent of properties falling under the landmarked status.

Brooklyn also features several neighborhoods with high percentages of landmarked property. Forty-five percent of properties in of Community District 2—which includes Brooklyn Heights, Downtown Brooklyn, Boerum Hill, Fort Greene, Clinton Hill, Fulton Ferry, and the Brooklyn Navy Yard—is set aside for landmark status.

REBNY's conclusion for the study was that the effect of recent landmarking is "chilling", and a "strong indicator that affordable units cannot be created on landmarked properties without significant assistance or incentives."

Yet the study also found that landmarked buildings rarely have an opportunity to impact construction. Citywide, only one hundred out of the 35,000 affordable units constructed between 2003 and 2012 were built on landmarked properties.

The notion that this is a major contributor to the unaffordability of our city is just laughable," Andrew Berman, executive director of the Greenwich Village Society for Historic Preservation told the Daily News.

Over the same ten year period, only 0.19 percent of nearly 63,000 newly constructed Brooklyn housing units were on landmarked properties and none were affordable. In Queens only 0.1 percent of the nearly 50,000 new housing units constructed were on landmarked properties.

The City Council's Landmarks Committee Chair, Peter Koo, said that the City takes into account the prospect of affordable housing during the landmarking process: "Maintaining and increasing the city's affordable housing stock is a priority I share with the de Blasio administration."