On a hot summer day, an urban flat roof can reach temperatures in excess of 150 degrees, a major contributor to the heat island effect in cities. Green roofs stay cool, about the temperature of the outside air. They provide habitat for birds, bees, and butterflies, and absorb rainwater so it does not become stormwater, decreasing erosion and pollution of the Chesapeake Bay. When we build, we try not to increase the solid or impervious surface. Green roofs are a beautiful way to do that.