Building owners now want more than stormwater control from their green roof systems.

By SAM BENNETT
Special to the Journal

When technology companies such as Amazon and Apple roll out plans for a new campus, architects, engineers and landscape designers must come up with cutting-edge solutions.

That’s because tech firms that make grand statements with their products want buildings that symbolize their futuristic visions.

These days, leading design firms such as NBBJ have added an essential team member to their line-up for tech-building design: horticulturists who advise on green roof designs.

Matt Wood, a principal with the Seattle landscape architecture firm SiteWorkshop, said horticulturists are critical to the success of any green roof project.

While structural engineers were working through the challenges of designing 95-foot-tall glass spheres in front of the new Amazon building in Seattle’s Denny Regrade neighborhood, Wood was busy analyzing the perfect balance of pumice, organics and sedums that will make up several green roofs on the Amazon project.

A horticulturist, Wood said it has taken decades of trial and error for green roof experts to refine the systems to meet clients’ goals for attractive spaces while also functioning property.

“A lot of the green roof systems are reasonably similar these days, so at this point it’s kind of a matter of dialing things in and refining the growing media,” Wood said. “Growing media” refers to soil foundations used to grow plants, trees and shrubs.

As green roofs have evolved, horticulturists and landscape architects have had to work through the challenges of balancing mineral contents in soil with silt, clay and pumice so that green roofs don’t become a host to weeds and create maintenance issues for owners, while also calculating hydrological issues so the roofs perform perfectly as they manage stormwater runoff, Wood said.

Greg Love, chief operating officer of Columbia Green Technologies in Portland, said his company uses hydrology software to calculate the percentage of stormwater that a green roof can handle.

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