Nestled into the Ouachita Mountains just east of the Oklahoma border, an evanescent treehouse greets visitors on the skywalk of the Mid-America Science Museum, in Hot Springs, Ark. Designed by Little Rock-based Wittenberg, Delony, & Davidson Architects (WD&D), the 275-foot-long elevated walkway takes museumgoers from the main building, which opened in 1979, up into the forest canopy, through the treehouse, and to a spiral platform and net suspended 30 feet above a stream.
The 10-foot-by-24-foot structure takes on a winged form, inspired by the insects of the Ouachita National Forest. WD&D director of design and project co-leader Chad Young, AIA, wanted it to appear as if “it could take flight.” When illuminated at night, the treehouse appears like a firefly with its white skin, dramatic butterfly-roof canopy, and cantilevered viewing platform.
Its ephemerality is amplified by the lightness with which it sits on the landscape, an effect achieved by careful siting, an emphasis on natural materials, and the use of slender structural supports. “It was a balancing act of making sure it’s a little bit hidden, and a little mysterious, but still very prominent and a real draw for museum visitors,” Young says.
Completed in 2015 as part of the museum building’s renovation and expansion, also by WD&D, the skywalk and treehouse were first proposed by Oakland, Calif.–based museum-exhibition design studio Gyroscope in a 2010 feasibility study. Early drawings showed a silver spaceship-like treehouse, but the firm felt the space needed to reflect the beauty of the site’s 10 acres of oak and yellow pine. They chose a material palette of pine, cedar, and Cor-Ten steel to blend in with the forest, and scaled back the size of the treehouse to simplify its engineering and to preserve existing trees. White acrylic panels and a bevy of galvanized steel turnbuckles provide lateral bracing (although some turnbuckles provide only visual contrast). The architects designed the treehouse in Autodesk Revit but also built a scale model illuminated by LEDs to test different lighting effects.
The treehouse’s steel frame was the most challenging design aspect, Young says. The thicket of small Cor-Ten tube columns seems to sprout from a series of monolithic concrete footings, embedded 6 feet into the ground. “There are no right angles,” he says. “All those posts and columns and branches are all at various angles, and nothing was repetitive.”
Six primary steel tube columns rise 30 feet and anchor the glulam beams that comprise the treehouse floor structure, as well as its roof canopy. The canopy is reinforced with galvanized steel cross-bracing. Walls, partially clad in cedar slats and punctuated with several large windows, are hung from timber joists and beams and steel channels braced off of the steel tube columns.
The southern wing of the butterfly roof cantilevers 22 feet, while the northern wing extends 15 feet. Anchored to the primary columns, the wings are constructed from a glulam-beam frame with an infill of pine slats. Joints are doweled, except for where the glulam beams are bolted with steel plates to the central rafter.
Construction took roughly five months and was complicated by the site’s running stream, not to mention the structure’s complexity. The steel detailer had fabricated the columns straight from the Revit model, but assembly was “difficult,” Young says. “Nothing was repetitive. We had to give [the steel erectors] a little tolerance on their connections to the wood beams. [We] sort of had to make it up as we go.”
For visitors, the treehouse is a multisensory experience. Spray misters cool visitors during Arkansas' hot summer days, shrouding the treehouse in a dreamlike fog, and a bench plays ambient music when visitors touch both armrests, completing the electrical circuit. Throughout the project, Young says there was an atmosphere of discovery even among the design team: “You’re imagining what it’s like to experience science from a kid’s point of view.”