City of Milwaukee's Green Roof
The City of Milwaukee will gain first-hand knowledge of the benefits of green roofs through a project recently completed at its 809 N. Broadway building downtown.
The project is a major step for the city that, since the 2005 creation of the Milwaukee Office of Sustainability, has been encouraging property owners to engage green building initiatives. The office is charged with coordinating efforts to improve Milwaukee's water quality, reduce energy consumption, and stimulate economic development in the green technology sector.
F.J.A. Christiansen Roofing was selected to install the green roof based on our green roof expertise the benefits and value of our TectaGreen turnkey solution.
“The city will realize several benefits from the green roof, the greatest being storm water management,” said Ted McNamara, FJAC vice president. Storm water runoff has been a problem for Milwaukee, especially where single sewers serve both sanitary and storm runoff needs. Those so-called combined sewers are in older parts of Milwaukee, including downtown.
The building houses the city's Department of Development and other offices, and was extensively renovated several years ago. But the 17,700-square-foot roof had since deteriorated.
“Green” roofing starts with tear-off |
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Beginning with the old roof, this project entails a number of “green” roof practices. The existing roofing was removed, with some of the old materials recycled. The rubber membrane was recycled under a new program sponsored by the EPDM Roofing Association. The old insulation and metal flashings were also recycled. And some of the existing ballast was saved for reuse on a penthouse portion of the roof. The city also is taking another additional step with the green roof. Temperature sensors were installed on the new deck, between the insulation and the soil, and at the plant level. The sensors will give the city solid data on the insulating value of the various components of green roofs.
TectaGreen turnkey green roof system |
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The new roofing system started with a two-ply vapor barrier to prevent building moisture from migrating through the concrete deck to the insulation.
Five inches of polyisocyanurate rigid foam insulation, with an R-value of 30, was then glued down with asphalt adhesive, followed by a 90-mil-thick EPDM membrane fully-adhered to the insulation. A protective fabric was then placed
over the membrane, followed by a root barrier to prevent the plants from affecting the roof membrane.
The planting system consists of drainage board that holds excess rainwater and which serves as a reservoir for dry periods, with a moisture retention mat over the drainage boards. The planting medium is then placed over the retention mat. The TectaGreen system involves a three- to four-inch layer of kiln-expanded shale mixed with organic compost. Based on a design, varieties of sedum are then planted in the soil, with pavers and gravel around the perimeter of the roof and crossing through the center.
The city has been posting progress photographs on its web site, from the tear-off to the plantings. Those photos can be seen at http://www.city.milwaukee.gov/GreenRoofHelpsReduce21961.htm .
With the project completed this summer, the plants will fill in the entire growing area over the next few years. But the benefits will be immediate. Chief among them is the storm water management benefit. “Although this is a relatively small roof in a large city, the benefits are very real, and this project can serve as an example to other building owners,” FJAC's McNamara said. On a traditional roof, storm water flows immediately to drains and then to a city's storm water collection system, in this case downtown's combined sewers. A green roof captures significant amounts of rainwater, and slows the release of excess water. That eliminates surges that can overwhelm a municipal runoff system. But for most rainfalls – those of about three-quarters of an inch or less, the green roof retains all of the water.
A recent 18-month study of green roofs in Seattle found that green roofs were able to reduce 65 to 94 percent of rain runoff. For the 809 N. Broadway building, it is estimated that for every inch of rainfall, the roof will prevent about 10,500 gallons of water from going into the sewer system. Because of that benefit, the Milwaukee Metropolitan Sewerage District provided a grant for a portion of the 809 N. Broadway building's green roof.
The city sees other benefits of the green roof, including reduced air conditioning costs made possible by the heat absorption and reflection properties of the plants. And in the winter, the city expects to see reduced heating costs, based on the insulation value and due to the plants' ability to reduce winds that contribute to building heat loss.
There are other, less tangible benefits, including aesthetics. For example, people who occupy upper-floor offices on the east side of City Hall as well as the M&I bank tower will now look out and see a garden where a dark, gravel-covered roof once was the scenery. Another benefit is the carbon dioxide consumption of the green plants, removing pollutants from the air.
While the installation cost of a green roof is higher than that of a traditional roof, a green roof can be expected to last twice as long, mainly because the planting medium is protecting the roof membrane from the deteriorating effects of sunlight.
“There are some very real, quantifiable benefits of green roofs,” McNamara said. “And there are some other benefits that are harder to quantify, but that nonetheless improve the livability of a community.”
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