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Courtesy Metcalfe Architecture & Design
Visitors are encouraged to lie on their backs in the Squirrel's Scramble and take in the greenery.


Up in the Air

Metcalfe Architecture & Design
Philadelphia, Pennsylvania

By Asad Syrkett
May 2012

In the age of the smartphone, getting kids excited about nature is increasingly difficult, says Alan Metcalfe, principal of Philadelphia-based Metcalfe Architecture & Design (MAD). So when the Morris Arboretum, which is owned by the University of Pennsylvania, approached MAD about designing a child-friendly walkway on its grounds, 50 feet up in a stand of oak, beech, yellowwood, and maple trees (among others), the firm jumped on the opportunity.


Location Philadelphia, Pennsylvania (Delaware River watershed)

Gross area 4,138 ft2 (385 m2)

Program Walkway and exhibition space


Architect Metcalfe Architecture & Design

Owner Morris Arboretum—University of Pennsylvania

Engineer CVM Engineers & Consulting (structural)

View all team & sources

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The resulting scheme is "Out on a Limb," a 450-foot-long exhibition dubbed the Squirrel's Scramble, that features viewing platforms, educational signage, and a web of high-tension rope suspended in the air. To compete with the simulated peril of kids' video games, Metcalfe explains, a stainless steel mesh called Invisinet figured prominently in the design: Viewing platforms appear to have no railings because they are wrapped with the material, which is nearly undetectable from afar.

In fact, the walkway, which was prefabricated and transported to the site, is incredibly secure, supported by a structure of 50- to 100-foot-tall pipes, all two to four inches in diameter and filled with concrete. "Believe me, we went through the wringer," Metcalfe says about the safety precautions. Attendance at the arboretum is up 66 percent since "Out on a Limb" opened in 2009. "People spend a lot of time sitting out there, interacting," says Metcalfe. "It's really magical."


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