NEW YORK—Accounting firm Grassi & Co. has expanded its space at 488 Madison Ave. to occupy the entire 23rd floor. The firm added 10,311 sq. ft. to the 13,081 sq. ft. previously leased for a total of 23,392 sq. ft. of space. Grassi & Co. will move into its new space in early 2013 after build-to-suit construction is completed.

Founded in 1980 and headquartered in New York City, Grassi & Co. is a full-service tax, accounting and business advisory firm.

Owned by The Feil Organization, 488 Madison Ave. overlooks St. Patrick's Cathedral and totals 447,000 sq. ft. Originally constructed in 1949, the property earned landmark status in 2010.