The Museum currently occupies the 52,000 square feet landmark 1908 Warburg Mansion and a 1962 addition. The six-story Warburg Mansion was retained and extended to replace the addition and its small courtyard entranceway. The 30,000 square feet expansion required approval of the Community Board, Landmarks Preservation Commission, City Planning Commission, Board of Estimate, and Board of Standards and Appeals. While the exterior of the existing Museum has been restored and scrupulously preserved, the interiors have been renovated and are used for galleries, bookshop / reception hall and staff offices for curators and administration. Meeting rooms and study areas are located on the upper floors. The formal entrance to the Mansion has been restored and is now used as the Museum's main entrance. The new layout achieves the Museum's goals of providing efficient, flexible space for this, the largest and most important institution of its kind in the Western Hemisphere. The new extension is the same height and continues the unified architectural character of the existing mansion by the use of the limestone materials and design features which distinguish C.P.H. Gilbert's 1908 structure.