A Desert Portal Made of Desert Materials: The Gateway to the McDowell Sonoran Preserve appears sprung from the earth.
Weddle Gilmore Black Rock Studio has developed a specialty in trailheads over its 10 years in business. The architecture firm has designed this building type for several municipalities near its Scottsdale, Arizona, base, and it has realized three for Scottsdale’s McDowell Sonoran Preserve alone.
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The Sonoran Preserve can be explored many times over, because its 36,400 acres boast dramatic diversity, says Weddle Gilmore cofounder Phil Weddle, AIA, LEED AP. “The landscape and geology changes dramatically from one end of the mountain range to the other, so we’ve tried to always be very micro-specific to each building site.” For example, at its first trailhead in this preserve, located at Pinnacle Peak, Weddle Gilmore riffed off the site’s signature boulders and decomposing granite: The design team transported a pile of boulders that had been excavated from an adjacent golf course development and applied the rock to the trailhead’s desert masonry wall construction.
The site of its most recently completed trailhead, the Gateway to the McDowell Sonoran Preserve, features the richest array of plant life in the Phoenix area, thanks to higher average precipitation. “We wanted to make sure we worked around the Palo Verdes, the ironwoods, and the saguaros,” Weddle says. Site development, particularly for the facility’s parking footprint, played an important role in minimizing intrusion. “We spent a lot of time mapping drainage and vegetation patterns, trying to find ways to nestle between those patterns.” The parking lot is semi-permeable, comprising four inches of decomposed granite with a mixed-in stabilizer.
Although Weddle Gilmore preserved arroyos and cacti, some earthwork alterations had to be made, such as grading the parking and building-foundation areas. In those cases the project team stockpiled the excavation material and reused it for the building itself. Ninety-five percent of the McDowell gateway’s 24-inch-thick walls are rammed earth salvaged from the site, combined with 5 percent Portland cement. (There is also a dowel-tied reinforced concrete bond beam positioned in the head wall.) The soil was sculpted into a shape that supports an asymmetrical butterfly roof, which channels 50,000 gallons of rainwater into a steel cistern that will handle all irrigation needs.
Darker-hued desert cobble also was retained from the excavation efforts, and besides repairing grading disturbances, most notably that salvage covers the building’s 8,500-square-foot butterfly roof. “It’s essentially working as ballast from a structural standpoint,” Weddle explains. And while he assumes that these several inches of cobble also provide some thermal mass, like the rammed-earth walls, “We really did this because we wanted the stealth effect. How the project is perceived visually against the mountain forms is one of the key drivers of the design.” The roof of the nearby equestrian staging area, also included in the scope of work, includes an 18-kilowatt photovoltaic array that supplies the facility with 105 percent of its electricity needs.
A trailhead’s program is fairly rudimentary—office, public restrooms, outdoor gathering spots, some interpretive elements. “But look at what a trailhead symbolizes, especially when Scottsdale’s residents voted twice to tax themselves to support the desert habitat,” Weddle suggests. The McDowell Gateway underscores residents’ sensitivity to the desert environment, and acts as a threshold to the preserve rather than as a distraction from it.
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