Environmental Protection

Allegheny County Will Verify Green Roof Effectiveness

Allegheny County, Pa., officials are facing an expensive wastewater system upgrade, and they hope that a green roof solution on an 87-year-old government building will manage area stormwater and lessen the severity of combined sewage overflows.

County officials plan to cover half of the building’s roof with boxes of plants settled in a growing medium. The area is as wide as a basketball court and twice as long.

In April, they began to build the green roof. They are equipping it with Web-based weather stations from Onset to monitor its performance.

“We can’t talk about the benefits of a green roof without monitoring it,” said Darla Cravotta, the county's special projects coordinator. “But when we have data, we can encourage other people to build green roofs,” she said.

Allegheny County has a team of four companies working on the project, which is being funded through the American Recovery and Reinvestment Act. The team includes Cuddy Roofing, Eisler Landscapes, IVC Architects, and Civil & Environmental Consultants, Inc. (CEC). The first three companies are working on designing and building the green roof, while Pittsburgh-based CEC will monitor a multitude of data points over the next six years.

John Buck of CEC will use eight Onset HOBO® U3O weather stations with approximately 90 sensors to track soil temperature, soil moisture, runoff duration, wind speed, wind direction, air temperature, relative humidity and solar radiation.

Originally, Buck wanted to use Wi-Fi communications for all eight weather stations. “But it turns out that Wi-Fi did not transmit through the roof,” he said.

Instead, he put two Ethernet-enabled U30s inside the government building and placed an access point on the roof so that the other six Wi-Fi devices up there could communicate. Buck is using Onset’s HOBOlink® Web server as a data repository and a way to monitor the system remotely, sensor-by-sensor.

The stations will be used to detect humidity spikes in several roof areas. The county administrators acknowledged that the 1923 building already had a history of roof leaks, a problem that could be made worse by putting structures up there. “There are people who are understandably nervous about more roof leaks,” Buck said.

If pre-set humidity limits are reached – which could suggest a possible roof leak – the station will automatically send Buck a text message alert. “We’ll get a message before the water starts dripping,” he said. “That wasn’t a primary objective of the project, but it is a benefit.”

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