Many roofs are made of asphalt. Since asphalt is a dark material, it absorbs heat from the sun. The plants on a green roof form a barrier that prevents a dark roof surface from absorbing sunlight and reflecting it as heat energy.
Did you know that the temperature on conventional city rooftops can easily reach 150° to 175°F or higher in the summer?
Yet the temperature on a green roof stays close to the temperature of the surrounding air. On a hot day, the temperature on a green roof can be 40° to 50°F less than on a conventional roof.