The museum opened a second major addition, this one designed by Philip Johnson and his partner, John Burgee, in 1977. The 1977 addition, which left the 1961 building and 1964 addition intact, expanded the museum's area by 36,600 square feet, more than doubling its original size. The expansion, which included a three-story section, enclosed the triangular space at the far western end of the building site, thus bringing the physical plant to its westernmost limit. Johnson's 1977 addition created an administrative wing, a 105-seat auditorium, a two-story storage vault, a spacious library, and two interior grassed courts that insulated occupants of the library and administrative offices from heavy traffic passing nearby.