From http://www.houzz.com/ideabooks/1708780/list?utm_source=Houzz&utm_campaign=u147&utm_medium=email&utm_content=gallery9

1. Reduced energy needs. A living roof acts as an insulator, reducing the energy needed to heat and cool your home or building.
2. Reduced greenhouse gases. Living green plants convert carbon dioxide to sugars, producing oxygen as a byproduct.
3. Reduced urban heat island effect. The cooling effect of evapotranspiration and the lower Solar Reflective Index* of a living roof result in lower overall heat given off by the roof surface. (*SRI: a measure of the energy a material absorbs, then releases as heat.)
4. Enhanced stormwater management. Slick, impermeable roofs shed water quickly and efficiently, contributing to both higher and faster peak runoff and flooding in densely developed areas. A green roof’s plants and soil slow both the rate and the energy of runoff.
5. Enhanced water quality. Plants and soil in a green roof absorb and break down pollutants in rainwater. The slower flow rate of stormwater equals less erosion and subsequent sedimentation downstream.
6. Added habitat. A living roof provides shelter and food for local birds, bees, butterflies and other fauna.
7. Improved value and curb appeal. This is a no-brainer — just look at the pictures!
8. Improved quality of life. Admit it: You’re happier when you’re surrounded by beauty … and I’d argue that most ordinary roofs fall in the category of blight rather than grandeur.