Support for the modular system of building construction, touted in the second half of the 20th century as the best basis for academic library building design, appears to be waning. A study of "green" libraries in 2008 revealed that not only has energy conservation become important, but that spaces designed for users rather than books have become paramount. The modular system worked particularly well for housing ever-expanding book collections, but collection growth is no longer a practical goal. Users want and need a greater variety of spaces, which purpose-built rooms are better at meeting.