Window installation is underway at 551 W 21, Foster + Partners' 19-story, 44 unit residential tower near the High Line. The white cast-concrete panels that comprise the solid portion of the facade were installed in the late summer through early fall. Window units feature a metal surround with generous amount of glass for the 11 foot ceilings in the apartments. Current progress on window installation has reached the seventh floor. The building is slated to finish construction in the fall of 2015.