Walmart builds big. And that includes a plan for a 40,600-square-foot “Ecoroof” for its 90,000-square-foot store now under construction in north Portland.
The green roof will become Oregon’s largest and serve as a testing ground to see how plants react in the moderate—yet elevated—urban climate and how the roof effects water runoff at the site. This is Walmart’s second foray into the mega-sized green roof world, already boasting the largest green roof in the world on a store in Chicago. Portland’s roof will be the second largest green roof in the U.S., according to the Arkansas-based retailer.
The Portland roof will cover the majority of the accessible area and consist of a layer of waterproof synthetic membrane root barrier, topped with a growing medium, followed by a layer of vegetation.
“Walmart’s Ecoroof will meet the City of Portland’s internationally recognized sustainable stormwater treatment requirements by decreasing runoff, saving energy and absorbing carbon dioxide,” says Kimberly Sentovich, a Walmart senior vice president. “The Hayden Meadows Ecoroof gives us an opportunity to test Ecoroof performance in a more moderate climate. We’re proud to help pioneer this innovation as part of our efforts to create a more sustainable world to help people live better.”
Located east of Interstate 5 near the Columbia River Interstate Bridge, the roof will be visible from community streets and by drivers traveling on I-5, as greenery will extend on the main portion and the lower section of the roof.
Walmart expects to use perennial plant sedum and cascading groundcover mixed with taller native plants on the edge. The hope is that the roof will also create a habitat for birds and insects.
Portland’s Bureau of Environmental Services plans to use the roof as a testing ground, especially for stormwater management, as Portland’s next largest green roof is 10,000 square feet smaller and is split up on the top of an apartment building in seven, 4,000-square-foot sections.
The Portland Daily Journal of Commerce reports that the city will run a three-year performance study, using the Walmart piece as an example. Other interested parties want to look at the differing soil depths and types on the roof, how varying plants handle the conditions and what other components—such as water feature or compost piles—could potentially impact the area.
While not every retailer builds to the same scale as Walmart, we’ll see how critical the data provided by the store’s roof becomes in future Portland planning.
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