although the library acquired an additional half-floor of space in the mid-1950s, the collection had outgrown its facility by the 1970s. the only available expansion space was a narrow vertical cavity next to the original library. schwartz/silver architects decided to suspend newly-added floors from roof girders which support the weight of the books from above, allowing the elimination of floor beams to maximize use of the narrow footprint. six new floors were fitted into the same height as the four of the original building, while still allowing for a vertical clearance for a truck turnaround below. a narrow, sky-lit atrium between the old building and the new addition allows sunlight to reach offices and studios in the upper floors, mitigating the unavoidable loss of exterior views. the result is an addition that has been referred to as a "glass cage", which contains the book stacks, limited-access collection, and exhibition gallery, while the renovated original bosworth building holds the main reading room and administrative offices.