Hanging Gardens: green roofs, stormwater management and bioremediation

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Until fairly recently the mention of a “green roof” elicited for me a mental image of Al Johnson’s famous restaurant in Door County. The sloping roof of that rustic log building sports a plush lawn with a small herd of goats casually munching on it. It is unabashedly romantic tourist bait. It is also a far cry from the technologically sophisticated contemporary green roof used to mitigate stormwater runoff in urban areas that are increasingly concerned about environmental sustainability.

I was introduced to green roof design by Peter, the Chief of Design Integration at a company that specializes in them called Hanging Gardens. The company is located in Milwaukee’s Global Water Center and we were standing on the spongy surface of its roof overlooking the Menomonee Valley. Although it was mid-summer the first thing I noticed was that the roof wasn’t particularly green. Instead of grass it was planted with multi-hued varieties of Sedum.

Peter explained that several species of Sedum are used because they are hardy and easy to maintain. The vegetation was set into a grid of waterproof containers, a little like the flats of flowers one sees at a garden shop. The whole array was divided into 12 sections called “slices,” which represent five different types of vegetated roofs. Some of the sections were as yet unplanted. One section was packed with what looked like brown sponges, obviously different from traditional soil that’s used in sod roofs like Al Johnson’s. The absorbent blocks are made from a combination of organic and inorganic materials that hold water longer than soil, Peter tells me, and the roots of the Sedum can grow directly into them.

Green roofs can provide a variety of benefits. Chief among them are reducing or slowing down stormwater runoff and filtering pollutants from rainwater. In some locations they can also reduce cooling loads on buildings, act as soundproofing, save money on energy, and even provide wildlife habitat or a place for agriculture. A side benefit in urban settings like Milwaukee is to reduce what’s known as the “heat island” effect. Cities become hotter than surrounding countryside because traditional building materials absorb and radiate heat from the sun.

Back in the Hanging Garden office I discover that the process of establishing the green roof had to weather its own problems. John, Chief Marketing Officer and company partner, picks up the story. It was his idea to move the company out of its previous location in the basement of his home. He was eager to bring his company’s expertise to the new and exciting enterprise of the Global Water Center.

The first hurdle to overcome was financial. Because a green roof had not been included in the construction budget, Hanging Gardens offered to help install a green roof that would become a research project utilizing grants from MMSD and the Fund for Lake Michigan. The second hurdle almost stopped the project in its tracks. Pulling up the existing roof revealed extensive damage from rot. Accommodating the 25 pounds per square foot required over the entire roof would have been prohibitive. The architects compromised, however, by rebuilding approximately one fourth of the roof with sufficient structural support for the test plots.

Green roofs are just one of the types of products and services Hanging Gardens offers. I am fascinated by a demonstration display of porous pavement, which is designed to allow rainwater to penetrate into the ground instead of running into storm sewers. A stream of water pours straight through without slowing down.

Both Peter and John are keen to show off a product called “GreenGlass,” a silica-based material that looks like exceedingly fine sand. “The raw product is dry, granular, odorless, hydrophobic and non-flammable,” says Peter. It’s also superabsorbent. When contaminants in water and soils come into contact with GreenGlass it captures them through hydraulic conductivity. “The dirtier the site, the better it is able to perform,” he assures me. A little like Depends for an incontinent society, I think to myself.

John points out the second floor windows towards the freshly landscaped Reed Street Yards. The series of bioswales installed along Freshwater Way utilize GreenGlass in a controlled test, he tells me.

John is decidedly bullish on his choice of locating in the Global Water Center. In 2013 Hanging Gardens became the first company to move into the incubator suites. He loves what he calls the synergy of the place, making connections not only with other people within the building but also with visitors who come from all over the world. He remembers when delegations from France, Germany, and England all came to visit in the same week. Then there was the time he went to a luncheon with a delegation from China, the CEO of Rexnord and the president of the Greater Milwaukee Committee. “That wasn’t going to happen in my home basement office.”

His enthusiasm also extends beyond the walls of the Center itself. On one side is Walker’s Point, which he observes is “the hottest area [in Milwaukee] for growth right now.” On the other side is the Menomonee Valley. “It’s incredible to have offices overlooking the Reed Street Yards and watching them being redeveloped,” he tells me. “We look out over the Sixth Street Bridge. I can see the Potawatomi hotel going up, the Harley Davidson Museum—the whole valley. It’s just very exciting to be in the middle of all this.”

“My ultimate goal is to have our company in a building over there,” he concludes, pointing again to the Reed Street Yards. “The valley has changed dramatically. There’s a lot of opportunity here and it’s exciting to see the possibilities. There are obstacles, too, because there are brownfields. But Hanging Gardens can help with some of those issues!”

This post is one in a series that relates to my Menomonee Valley Artist in Residency. For more information about the residency and links to previous posts and photographs, go to MV AiR.