Having received the largest grant in the history of the Massachusetts Board of Library Commissioners, $10.7 million, the Cambridge Public Library restored its 27,200 square foot landmark main building and expanded it with a striking 76,700 square foot glass-enclosed addition. A decade-long undertaking, with a total project cost of $90 million, the library opened in October 2009.

Susan Flannery, director of libraries, architects William Rawn Associates and Ann Beha Architects, and the 18-member Design Advisory Committee based their vision on the principles of transparency, inclusiveness, and sustainability.

The main feature exemplifying those principles is the 180'-long, 42'-high double-skin curtain wall—the first comprehensive U.S. application of such a system by Gartner Steel and Glass GmbH, based in Würzburg, Germany. It transmits daylight deep into the building, maximizes thermal comfort in reading areas along the glass, provides a connection between patrons and the civic park just outside, and saves energy.

The double-skin system consists of inner and outer glass walls separated by a three-foot-deep multistory flue cavity—a passageway for directing air currents—that works like a chimney. Its movable sunshades (which also act as a light shelf to reflect daylight onto the ceiling and deeper into the space) balances the light levels to avoid glare.

That double-skin façade is only the most noticeable sustainable feature of the structure, which has been submitted for Leadership in Energy & Environmental Design (LEED) certification.

Other green strategies include open space enhancements that increased the park area by half an acre; the 33,000 square foot green roof with four inches of soil to allow tree planting; a 400,000-gallon neighborhoodwide storm-water management facility; a construction waste recycling program that diverted 95 percent of construction waste from landfills; and the use of low-VOC paints, adhesives, carpeting, and other materials.

The original building, listed on the National Register of Historic Places, also received a face-lift, care of Ann Beha Architects. The original façade of brownstone and granite was cleaned and restored, the stone porch entrance was transformed to include an outdoor seating area, and major spaces within the library were renovated to include an Information Commons and a YA room and lounge.

During the programming stages, participants searched for a way to connect the new wing with the historic building. The solution was to divide the new wing into four zones that run lengthwise and parallel to the curtain wall. The center zone acts as a Main Street, housing the circulation and service desks and running through the addition and the historic wing, which largely consists of reading and computer areas.

At the library opening, over 1700 residents gathered and checked out 5000 items by the end of the day. The hybrid nature of the facility—with elements of both a bookstore and a library—make it possible for users to find a quiet area to read and study or a social space to talk and eat or drink. Flannery notes that "there is an intuitive quality about these spaces and it has worked amazingly smoothly."

Circulation is up 70 percent over the same period last year, and program attendance for library-sponsored events is up 175 percent. More twentysomethings are taking advantage of the free Wi-Fi, while the teen lounge "has been successful beyond our wildest imaginings," says Flannery. "The most reliable manifestation of success is that the library is filled from opening to closing each day with residents of all ages. All parts of the building are equally used, with individuals finding just the right space."

With the historic wing restored and its interior spaces reconfigured to adapt to modern times, the glass addition welcoming visitors and patrons, open and accessible spaces throughout, and sustainable strategies, Cambridge Public Library has redefined what it means to be the "civic heart" of the community.