The society just released a report showing the power of plants. It turns out the roof prevented more than 27,000 thousands of gallons of stormwater – nearly 75 percent of all precipitation on the roof – from running into the overworked sewer and stormwater system.

It also reduced building energy costs by hundreds of dollars a month, lowering energy usage in the winter by 10 percent and by about 2 or 3 percent in the summer. And the green roof lowered air temperature by as much as 32 degrees in the summer, a huge dip compared to the city's abundance of scalding tar roofs, which helped mitigate the urban heat island effect.

The full report can be found on the ASLA website.