Toronto was the first North American city to pass a green roof law, in 2009, requiring new buildings or additions that are greater than 21,000 square feet to cover between 20 and 60 percent of their buildings with vegetation. Meanwhile, the U.S. government’s General Services Administration has over 80 buildings with green roofs, spanning approximately 2.2 million square feet, which is about 48 football fields of green roofs. This includes what is believed to be the second largest green roof in the world: the U.S. Coast Guard Headquarters in Washington, DC, about as large as 10 football fields.Today in the US, there is more than 17.5 million square feet of planted roof surfaces, which is music to the ears of my guest, Alan Burchell.Alan launched his company Urbanstrong in 2014 to promote rooftop development strategies that integrate nature back into cities. Based in the Brooklyn Navy Yard, Urbanstrong provides finance, engineering, design, and construction services for green roofs and to date has installed hundreds of thousands of square feet of green roof and wall projects throughout the northeast, on schools, offices, restaurants, apartment buildings, and brownstones.Alan is an engineer by training, with an MBA and a masters in sustainability management from Columbia University. He previously worked for the wind energy company Siemens Gamesa and is cofounder of the New York Agriculture Collective.In this episode, Alan joins me to discuss the state of green roof installations in the US and abroad, the challenges as well as the most promising strategies to a greener rooftop future.