'Green roofs' designed to provide cleaner water, less runoff

Seattle Public Utilities (SPU) has started a collaborative effort to study the effects of "green roofs," which use natural plant life on building roofs, on storm water flows and runoff water quality.

On March 8, SPU showed off the first green-roof building from which it will record observations, the Zoomazium at Woodland Park Zoo. This building, which was completed in May 2006, is the first of many featuring green roofs from which SPU will use to gather information.

"It's a timeless technology," said Brendan Connolly, of Mithun architects, responsible for designing the Zoomazium.

"It's just starting to take root in America," he continued, adding that many European countries have used the technology for years.

One reason for its growing popularity in Seattle, according to Con-nolly, is to see if it can have an effect in reducing the pollution that occurs in local bodies of water as a result of storm runoff.

"We're looking to preserve local salmon habitats, as well," Connolly said.


Hoping to see a dramatic change in the amount of runoff, SPU hired Taylor Associates Inc. to oversee and record measurements from the Zoomazium project. Taylor Associates is a local aquatic-sciences consultant, and while it has taken preliminary measurements, it has yet to run any analysis.

Several instruments, including roof-runoff monitoring sensors and water-quality sampling equipment, are in place atop Zoomazium and taking constant measurements.

"We're hoping to get two samples this month," said Bryan Berkompas, of Taylor Associates, adding that it all depends on weather patterns.

The green roof in Woodland Park Zoo is the first of four such projects that SPU is involved with. Others, including the Ballard City Library and Seattle City Hall, have green roofs already, but they have not yet been studied.

"If we want to have a greener environment, with less greenhouse gases and contamination, one of the best ways to do that is to engage with the design community," said SPU resource conservation planner David McDonald.

Green roofs such as the one at Zoomazium require a number of different layers of material to function atop a building roof. Layers of plywood, insulation and a rubberized membrane are set between the roof and the plant life to keep the building itself dry.

Then, a drainage mat, which filters the water from the slanted roof down into a trough, sits below 6 inches of mixed soil.

The plant life on top of Zooma-zium - all Northwest plant species - includes sword ferns, blue-eyed grass flowers and nodding wild onion.


This project follows the signing of the Seattle Green Factor by Mayor Greg Nickels in December, which requires businesses in Seattle's neighborhood business districts to increase the amount of plant life within their properties.

One of SPU's main goals in studying green roofs is to gain insight on creating citywide storm-water management policies in the future. As a result, many local businesses have begun to show great interest in using green roofs.

"We've begun to put on presentations with the Department of Planning and Development," said Mc-Donald, adding that concepts such as "green walls" are also viable options.

For more information on green roofs, visit www.seattle.gov/dpd/GreenBuilding.

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