The value of rental apartment buildings has remained strong, despite a recent drop in rents. The chairman of Massey Knakal Realty Services, Robert Knakal, said that apartment buildings with values under $50 million are holding steady in price. According to Reis Inc., the city’s market-rate, investment-grade apartment market “remained extremely tight in the first quarter of 2008, with the lowest vacancy rate among the top market.” Some new rental buildings in Lower Manhattan are doing well. At Glenwood Management’s new 396-unit Barclay Tower (across the street from the Woolworth Building), nearly all of the apartments have been leased. Just a handful of the 163 rental units are available at 89 Murray Street, at Greenwich Street.