- North American green roof and wall industry association Green Roofs for Healthy Cities (GRHC) has dubbed Washington, DC the city with the greatest square footage of green roof installations in 2017. The District registered more than 1 million square feet of green roofs.
- Newark, NJ was the next closest city with nearly 600,000 square feet of green roofs. The cities rounding out the top 10 are New York City; Seattle; Portland, OR; Toronto; Philadelphia; Chicago; Culpeper, VA; and Gaithersburg, MD.
- The 2017 green roof survey collected data about more than 1,000 completed projects in 39 states and five Canadian provinces. The survey recorded nearly 5.4 million square feet of green roofing, but the actual number could be higher because not all GRHC members take part in the annual survey.
Generally speaking, green roof status involves creating a permanent greenery area with a waterproof base on a building's roof or a mid-building patio or ledge. Simply adding some potted plants does not count.
Green roofs are considered to have numerous benefits, the obvious being the environmental benefits of vegetation that include filtering out pollution, providing habitats for wildlife and lowering urban temperatures to mitigate heat islands. They also are touted for absorbing rainwater and improving drainage, which is a growing tactic for boosting cities' flood resiliency. Green roofs additionally can provide insulation to increase buildings' energy efficiency. Plus, they offer an aesthetically pleasing, calming environment for employees and residents, which can improve health.
City buildings increasingly sport greenery high above street level, partially counteracting the lack of foliage at street level in many cities. These elevated gardens will become more important to cities as urban population numbers continue their steady incline and developments vie for space, putting green space increasingly at risk. Cities including San Francisco, Denver and New York all have measures to encourage or mandate green roofs on urban buildings.