Mercer Slough Environmental Education Center
Teaching in Trees: A new Washington Nature Center elevates its educational mission literally preserving fragile ecosystems on the ground and lifting visitors into the forest canopy.
It’s a classic design problem: How do you get people out into nature without destroying the very thing they have come to appreciate? This was a central challenge for Jones & Jones, designers of the LEED Gold-certified Mercer Slough Environ-mental Education Center (MSEEC) in Bellevue, Washington. The clients, a partnership between the City of Bellevue and the nonprofit Pacific Science Center, wanted an interpretive center that would truly immerse visitors in their natural surroundings. The proposed site was covered with mature trees, steeply sloped, and positioned just above a sensitive wetland—Mercer Slough, a 320-acre gem protected by the city.
Rather than compromising the site by creating a conventional single-building facility (which would have required grading and filling), or limiting the educational mission by choosing a different location, the team broadened their thinking about the site into three dimensions. The result is a unique collection of seven shed-style buildings, elevated above the forest floor and threaded through open spaces in the forest canopy, connected by aerial boardwalks that traverse the upper story of the woodland without disturbing the ecosystem on the ground.
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As visitors descend the terraced slope from the welcoming plaza toward the center and the slough—a slow-moving wetland between Lake Washington and Puget Sound—road noise falls away and the experience of being in the understory deepens. Farther along, expansive views over the slough to the city from various lookout points along the boardwalk provide both an intimate experience with nature as well as a sense of place within the larger community—an important component of the center’s goal of strengthening the city’s stewardship of its natural surroundings. “What we hear most often from visitors is that they feel like they’re outdoors even when they’re inside,” said city park ranger and MSEEC environmental education coordinator Christina Dyson-Farrell. “The kid inside everybody enjoys a treehouse. To have the architecture bring forth that sensation is very special.”
That “treehouse” sensation is made possible by a system of helical pilings, which were salvaged from a natural gas drilling operation, and concrete pile caps that lift the building foundations off the forest floor—anywhere from four to thirty feet—allowing water flow as well as resident fauna to pass underneath. The center is surrounded by mature trees—predominantly bigleaf maple, Douglas fir, and some cottonwood. Dense deposits of clay in the soil left pockets where trees would not grow, creating open spaces in the canopy where the buildings could be placed, and allowing the team to leave nearly all the existing trees standing—a move that would also prove critical to the objective of ventilating the buildings naturally. “We started with the site and asked how much the site could carry,” said Mark Johnson, AIA, of Jones & Jones. “It wasn’t just a tree conservation effort—it was about inserting the education center directly into the tree canopy.”
For a project with wetland education built into its mission, stormwater management was a crucial design driver. With site soils that had not previously been impacted, the team sought a way to let the ground remain “light and fluffy”—essentially, to let the ground be their stormwater management system. Leaving the site’s existing contours intact and raising the buildings off the ground allows stormwater to flow around and underneath the “spider leg” pilings. All soil retention is done with gabion walls—rock fill enmeshed in wire enclosure—through which stormwater is filtered. Rain that falls on the building roofs is directed to the gabion walls through gutters installed along the boardwalk railings, where they become a prominent and sometimes interactive display of the stormwater-management efforts. Dyson-Farrell says the gutters attract the attention (and inquisitive hands) of visitors young and old. Farther down the line, bioswales and compost-amended filter strips provide additional lines of defense to remove sediments and contamination from runoff before it reaches the slough. “People are seeing where their water is going,” Dyson-Farrell said, and cites the system as a valuable tool for watershed education.
Other opportunities to build educational features into the design presented themselves at nearly every step. The spare interior aesthetic made it possible to leave utilities and conduits uncovered, offering a lesson in how buildings work. Boardwalks not only connect the buildings to one another, but also branch off into overlooks that serve as individual outdoor teaching spaces—one group can stand at one overlook to talk about how stormwater impacts the watershed, while another group can be immersed in a lesson about forest ecosystems.
The design team took advantage of the site’s microclimate to help keep the buildings comfortable and minimize energy use. Light-colored roofs on five of the buildings (the other two have green roofs) reflect solar radiation. Meanwhile, extensive tree cover keeps the area shaded and cools the air surrounding the buildings, which are naturally ventilated using windows controlled by carbon-dioxide sensors—the “lung,” as Johnson calls the large, silver, sensor-activated louver that adjusts the ventilation. (This ventilation system was put to the test during the Northwest’s heatwaves in the summer of 2009; Dyson-Farrell said that with a few exceptions, most of the buildings stayed comfortable.) “The city realized that these trees were their air-conditioners,” said Johnson. During cooler months, the buildings are warmed by hydronic radiant heating (with the exception of the restroom buildings, which use electric wall heaters), powered by gas-fired condensing boilers that are 92 percent efficient and operated by digital direct controls (DDC). Walls are wood-framed using two-by-eights and insulated with cellulose to nearly R-30, and floors are structural insulated panels (SIPs) with an R-value of 48. The SIPs reduce thermal bridging, but they are also low in thermal mass, which presented some difficulty in keeping the buildings consistently warm enough on cloudy winter days—a problem that the team resolved by implementing the DDC system and commissioning the controls.
On a project that went to great lengths—and sometimes, great expense—to preserve onsite ecosystems, creative cost-saving measures were in high demand. Johnson credits the contractor for coming up with many of these, citing in particular a solution for the problem of peaty soils in the planned lower-level parking area. Instead of installing a layer of EPS foam subsurface and paving with asphalt, the contractor proposed preloading the soil by stockpiling all the fill for the project onsite through the winter before construction—a no-cost alternative to the much more expensive EPS-and-asphalt option. This parking area, just a few feet above the slough, represents another stormwater-conscious strategy: Rather than clear and pave a larger parking area, the team chose to weave smaller pockets of parking into the gaps in the trees, keeping the total parking area to a minimum and encouraging the use of alternative transportation.
The MSEEC was created to bring people in touch with nature and deepen the community’s sense of place. By all accounts, it’s succeeding—more than twice the number of expected students and visit-ors have come to walk the trails, attend meetings or educational programs, or see the buildings perched among the trees. The hope is that interest will continue to seep into the community—and beyond. “You always hear about how one drop in the water creates all these exciting ripples,” says Dyson-Farrell. “It’s incredible to see the ripples spreading from this place.”
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