R6 residential districts are widely mapped throughout New York City. They are medium-density residence districts consisting of multi-family apartment buildings, and most commonly found in neighborhoods throughout Brooklyn, Queens and the Bronx. Neighborhoods in R6 districts can have a variety of building types depending on height factor regulations and Quality Housing regulations, though building heights generally don’t exceed 13 stories. (nyc.gov)
The floor area ratio (FAR) in R6 districts can vary between 0.78 for single-story buildings to 2.43 for a typical 13 story building. The height of buildings is also dependent on the open space ratio, which in R6 districts can range from 27.5 to 37.5, which is expressed as a percentage of the total floor area of the building. Usually, the taller the building, the more open space will be required on the lot. (nyc zoning glossary)
Some R6 districts also fall under Quality Housing regulations, which are areas with height limits between 6 to 8 stories imposed in order to maintain the character of many neighborhoods with older buildings. R6A districts are areas where Quality Housing regulations are mandatory. The regulations produce high lot coverage, with buildings allowed to come closer to the street line. The floor area ratio in these areas is 3.0, though higher maximum FARs are available for buildings that participate in the Inclusionary Housing Program. R6B districts, which include areas like Park Slope and Bedford Stuyvesant that are known for their 19th century brownstone architecture, have a FAR of 2.0 and may not exceed a height of 50 feet.