Silverback Development and an unnamed partner are planning to develop a 13-story, 65-unit residential building at 351-359 Second Avenue, located on the corner of East 21st Street in Gramercy. The project will measure roughly 80,000 square feet and rise 145 feet, Crain’s reported. The residential units will be condominiums ranging from studios to one-bedrooms, although the developer could possibly configure the apartments to be larger. The 8,052-square-foot assemblage is occupied by three low-rise buildings. The developer plans to begin construction next year and open the building in 2020.