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Out on a Limb, Tree Canopy Walk, Morris Arboretum of the University of Pennsylvania, United States

Thursday 08 Sep 2011

Take a walk on the wild side

Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States
Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States Out on a Limb, Tree Canopy Walk by Metcalfe Architecture & Design in Morris Arboretum of the University of Pennsylvania, United States
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09/10/11 Reem.O, sharjah
This could be one of the most innovative ideas i have seen so far.Imagine the thrill walking between the tall trees!! it might not be a building but it sure serves the community, and the structure is superb in terms of material use and technique of interlacing the structure with the wild itself.
Award Entry

Metcalfe Architecture & Design have built a tree canopy walk creating an enticing exhibit experience 

Out on a Limb is a critically acclaimed, award-winning 450-ft tree canopy walk at Morris Arboretum of the University of Pennsylvania that transports visitors from walking on the ground to walking in the treetops five stories above the forest floor without steps or ramps. It features a pavilion, suspension bridge, giant hanging bird's nest, two rope netting 'wading pools in the sky' and dramatic vistas that change seasonally.

It is a perfect example of Metcalfe Architecture & Design's interest in using architecture to create enticing exhibit experiences. The team used steel, wood, and netting throughout the structure's 4,138 square feet to create a series of architectural experiences - compressed entry, forced vistas, linear movement, various forms of enclosure, manipulation of natural light, and rhythm - 50 ft in the air.

While they were charged with creating an educational exhibit, they emphasized the experience of being IN the trees over reading text about them. Their goals were to celebrate the human experience using play, discovery, and social interaction, and to give families the unique experience of being 'up in the trees.'

The architects created visceral sensations of fun, anticipatory risk - the thrill of height, unique juxtapositions, sway and vibration, and combined a gradual falling away of the ground below with the structure's lace-like transparency.

Morris Arboretum is a 92-acre public and research garden in Philadelphia and the official arboretum of the Commonwealth of Pennsylvania.

Metcalfe Architecture & Design worked closely with Morris staff to design an attraction that would achieve its goals of increasing the number of family visitors and membership, boosting its admission income and visibility, and broadening its age and social demographic. It was clear that children drive family attendance and loyalty; if children were interested, their families would visit. The new attraction also had to resonate with the Arboretum's mission of illuminating the relationship between urban trees and people, and enticing the full age range of family visitors.

Through focus groups and polling hundreds of children and their parents, the theme of risk jumped to the top of the agenda. Of course, parents wanted their children to be safe, but the message was clear - to engage kids between four and 18 years old, especially in this world of hair-raising digital games and movies, they had to provide them with a compelling, emotionally rich experience with trees. The team needed to offer the chance to take risks in the woods.

Climbing trees is a joy many of us remember from our youth. As stewards of a living collection - a 'museum' of trees - and responsible managers of a public facility, that was not an appropriate option.

Morris' market research indicated that an attraction luring children with a sense of thrill and perceived danger and adults with the romance and sentimentality of youthful tree climbing memories could bolster long-term membership.

Morris Director Paul Meyer was moved by a simple exhibition he saw in London's Kew Gardens 10 years earlier, of construction scaffolding erected 30 feet into the trees. Visitors climbed stairs into the tree canopy and experienced a wholly different world above. This simple attraction was a smashing success and Paul thought that something akin to this would be a winner at his institution.

Throughout the conceptual, design, and construction process, the team regularly met with multiple constituent groups, including end-users; Morris board and staff members, from the departments of development, education, horticulture, and maintenance; university officials; community members; and code enforcement and zoning officials - presenting their ideas and collaborating with them to create a safe, exciting, educational and easy-to-maintain structure.

The outcome was Out on a Limb, a tree canopy walk that is the central highlight of the multi-station Tree Adventure exhibit designed by us for Morris.


The architects were intent upon creating a social space where visitors are able to enjoy their character as social animals. They pushed people to interact using walkways of minimal dimension, a bird’s nest that creates an intimate space for children, a netting area that creates a “wading pool in the sky” where visitors dangle their feet, or perhaps roll to the bottom of the nets 50 feet above the forest floor, inevitably creating physical contact between visitors. Once someone breaks this social barrier, conversation begins. The team expected families to interact but were pleasantly surprised to all see friendly interactions among strangers.

The team was also committed to creating a welcoming and challenging experience for all visitors. By carefully leveraging site conditions they created a virtually flat walkway, wide enough to accommodate crowds and wheelchairs and strollers while maintaining the perception of transparency and close edges. Without sacrificing the sense of perceived danger, people of all abilities are confronted with new ways to experience the forest. Plus, they knew children would want to return if they had power over their parents. The architects consciously devised places where the kids might venture further than their parents, such as hiding in a dangling bird’s nest, or running and jumping into the netting before their parents could.

Additionally, this project is unusually successful in attracting a wide visitor demographic, including the elusive teenager, typically allergic to anything that attracts young children and families.

Finally, the team focused on creating a playful exhibit space that secretly teaches visitors about the outdoors, the world of the trees and animals above us. It does so with minimal use of descriptive materials, instead depending on architectural manipulations to use the thrill of height and perceived risk to heighten visitors’ awareness of their environment. On the tree canopy walk, visitors learn about the world through unprogrammed experience, investigate through personal play, and broaden their vision through introspection.


“Out on a Limb” has been a huge success in boosting revenue, attendance, publicity, and acclaim as indicated in the arboretum’s 2010 Annual Report:

‘The opening of the Tree Adventure exhibit … set the stage for the Arboretum to surpass annual and monthly attendance records. Total visitation was 128,503, moving the Arboretum up in the ranks among Philadelphia’s most popular family cultural destinations…Program and garden visitation increased 33%. This past year, 10,000 more children had fun connecting with trees, family and friends at the Arboretum. As a result, membership also reached record levels. Gate revenue increased 33%, a significant growth in income during a very difficult economy. For the first time, more than one-third of visitors were children in FY 2010’.

Morris Director Paul Meyer said:

‘Tree Adventure has exceeded our expectations it is fun adventuresome, and exciting without being overly didactic. As we live more and more in the cyber world, our busy lives and electronic devices often distance us from nature and one another. Real experiences in nature are increasingly rarer. Our Tree Adventure exhibit enhances that very personal experience, connecting our visitors not only with each other but also with trees and the natural world, encouraging them to see what’s really around them’.


The structure is built on a hill in the middle of a “museum” of trees. The delicacy of the collection made it imperative that we not attach the structure to the trees or disturb their root systems. The architects used micro-pile foundations, 150 feet deep and six inches in diameter, threaded through roots systems located with a giant leaf blower.

components (especially the structure) were factory -fabricated off-site and placed by a 150-ton crane to minimise site impact and environmental pollution. The materials are sustainable in that the wood is mostly locally obtained (black locust, cherry, and cedar) and the steel is recyclable. LED and low-voltage fixtures (halogen and metal halide) illuminate this structure.

The ever-changing forest required a sustainable and changeable design. Trees fall and perish. All sections are structurally independent, and can be relocated by crane to new stands of trees if necessary.

Key Facts

Status Completed
Value 0(m€)
Metcalfe Architecture & Design
Reinventing Cities

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