The amount of space available on paper in some of New York City’s office buildings might shrink due to the recession. Real estate professionals sometimes increase the square footage of an office space by including the “loss factor,” or the part of the space that isn’t usable by the tenant, in the square footage number for the space. At 530 Fifth Avenue, for example, the sixth floor of the 26-story building had 24,400 square feet of space when the building was completed in 1957. Today, according to real estate database CoStar, the sixth floor has 34,706 rentable square feet. As the commercial real estate market slumps, office landlords and tenants may start modifying square footage measurements to what they were in the past, in order to lower rent and utilities costs.