Glass building enclosure
An innovative system of insulated glass will enclose the new Central Library. On surfaces of the building that receive the most sunlight, an expanded metal mesh layer within the glass will reduce heat and glare, while retaining visibility.
Why glass?
A key concept for OMA/LMN's design of this important civic building was to be transparent and open. The solid floor areas are connected with a glass enclosure that allows passersby to see activity in the building and the different program components in the building, such as the Books Spiral.
The visibility of the building's interior and the appearance of the exterior will vary with the lighting conditions outside - whether it's clear and sunny, overcast, or it's nighttime.
The architects evaluated a number of different glass materials, balancing both aesthetic qualities and energy performance. A large mock-up was built at the old Central Library as a way to review full-scale samples of various glass types. Alternatives were mounted in a large framework to simulate the orientation in which the glass would be seen when the building was constructed.
Metal mesh selected
After considerable study, the metal mesh glass was selected for those surfaces receiving direct sun. The glass, cut in approximately 4-foot by 7-foot diamond-shaped units, promotes energy efficiency by letting in natural light and reducing the need for artificial light. OMA/LMN conceived of the expanded metal mesh as a device to reduce glare and heat. The metal mesh - aluminum sheet metal that is cut and stretched and placed between layers of glass - will be used on approximately half the building exterior. The rest of the building skin is comprised of clear glass. All the glass includes low-emittance coatings for improved energy performance. The glass units were tested by computer simulation and actual physical tests. The glass assembly is very strong. It passed all wind, rain and air infiltration tests and met all codes for earthquake resistance.
Such glass units are used on many office and commercial buildings. The metal mesh inserted in the glass units has been used in Europe, but the library will be the first example built in the United States.
Building form designed to control light
The library's building form was specifically designed to control the type and quantity of sunlight. Library program functions were placed where they would receive appropriate light. The Norcliffe Foundation Living Room, for example, faces south, which means the room is filled with daylight, filtered by the metal mesh layer. The Betty Jane Narver Reading Room, however, faces north and it will have more controlled light with less glare, which is more conducive to reading. Some extended portions of the building provide shade to other portions.
Installation
The diamond-shaped glass units arrived at the site fully assembled and were installed onto a steel structural framework. Crews installed the units from the top of the building down. A tarp was placed over the building as the glass exterior was installed, providing weather protection as work continued. The subcontractor for the glass exterior was Seele Limited Partnership, based in Germany. The glass manufacturer was Okalux, also from Germany.
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