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Perforated Panels Renew Library

Bonnells Rinconada 1

Double-layered sunscreens create dynamic interior shadows

Photo: Cesar Rubio, www.cesarrubio.comPatterns can become part of a building's identity. At Rinconada Library in Palo Alto, Calif., circular and T-shaped elements are incorporated throughout. On a macro level, the building's footprint is T-shaped. Zooming in, terra cotta sunscreens with a grid of bisected circles enclose courtyards on three sides. The same circular pattern on the terra cotta is repeated on light panels in the interior. Additionally, there are round pedestal gardens and a large, circular planting bed on the site.

When it came time to renovate and expand the library in 2013, South San Francisco, Calif.-based Group 4 Architecture, Research and Planning Inc. picked up on the circular pattern to develop double-layered, perforated aluminum sunscreens.

The custom sunscreens met several goals. In addition to the practical need to shield intense sunlight, the project had to be sensitive to the building's original design. Edward Durell Stone designed the library, then called Palo Alto Main Library, for construction in 1958. Group 4 was tasked to develop a plan that complemented Stone's design and differentiate the new parts.

In plan, the historic wing forms the top of the T, oriented north-south. The addition extends east, forming the stem of the T. The project expanded the library approximately 4,000 square feet, bringing it to 30,000 square feet. When the LEED Silver-certified project was completed in February 2015, it was renamed Rinconada Library.

Jonathan Hartman, LEED AP BD+C, principal at Group 4, says, "Reflecting on the role of the patterned terra cotta block screenwalls around the existing building and their role in light control, we started thinking about a patterned screen that was elevated above the ground plane to preserve views into and out of the building, while helping to control high-angle solar exposure. Both the historic and new wings of the expanded library feature a new translation of the circle pattern's geometric language."

Photo: Cesar Rubio, www.cesarrubio.comMokena, Ill.-based Architectural Grilles and Sunshades Inc. (AGS) fabricated, and Hayward, Calif.-based Capitol Glass Co. installed, Newnan, Ga.-based Bonnell Aluminum Extrusion Co.'s aluminum into 3/16-inch-thick panels with water jet-cut perforations for the double-layered sunscreens. The panels were powder-coated to match the Atlantic Gray of Norcross, Ga.-based Kawneer Co. Inc.'s storefront windows. Additionally, AGS fabricated 2-inch by 6-inch rectangular aluminum tube spacers and 1-inch diameter stainless steel stand-offs for the project.

"From the beginning, we felt that the screen wanted to have a depth to it and we liked the interplay of two layers working together to create a sum result that was far greater and richer than what you experienced with each layer independently," Hartman says.

To come up with the optimal perforations, Group 4 completed numerous studies including a scaled model of the final option and a full-scale mockup of a panel face. "We explored a wide variety of patterns, pattern densities and screen heights before arriving at the final solution," Hartman says. "The iterative process was essential in honing in on the right size and scale of the circles and their relationship to each other between the two faces of the screen. The circle pattern in each layer is based on a custom algorithm designed to create dynamic shadows inside the space that mimic the quarter circles of the historic terra cotta screen."

Photo courtesy of Group 4 ArchitectureSpecial consideration was given to installation. Capitol Glass bolted the panels to the sloped, primary steel structure with custom brackets. "In the design of the mounting brackets, we anticipated the need for field adjustments at each bracket to address construction tolerances between the primary structure and the screen, which ended up working very well," Hartman says. "In the new wing, the sunscreen runs horizontally around the eaves, suspended to a level aligned with the top of the historic terra cotta walls. This creates a floating-roof effect and a complementary architectural composition with the historic structure."

The aluminum panels required hidden slip joints to accommodate thermal expansion across the continuous length of the south-facing span. "In the historic wing, the dual-layer metal sunscreen is suspended from the eaves in a vertical orientation to screen the new glass-enclosed group study rooms," Hartman says. "In this location, the sunscreen comprises de-mountable panels to permit cleaning of the exterior of the glass. Additional rigidity was required for the screen in this application, as well as standoff supports incorporated into the window wall structure."

Rinconada Library, Palo Alto, Calif.
Owner: City of Palo Alto
Architect: Group 4 Architecture, Research and Planning Inc., South San Francisco, Calif.,
General contractor: SJ Amoroso Construction Co. Inc., Redwood City, Calif.,
Glazing/sunscreen installer: Capitol Glass Co., Hayward, Calif.,
Fabricator: Architectural Grilles and Sunshades Inc. (AGS), Mokena, Ill.,
Aluminum: Bonnell Aluminum Extrusion Co., Newnan, Ga.,
Storefront: Kawneer Co. Inc., Norcross, Ga.,

Photos 1, 2: Cesar Rubio,
Photo 3: Courtesy of Group 4 Architecture