Weeds on the roof?

Anyone who has ever fought moss on a wet, shady old roof might wonder why the school department is letting green stuff grow on the roof over the entrance to the new East End Community School. The green stuff is a collection of sedums, native grasses, and flowering plants installed in a specially designed bed on the roof over the entrance. It is designed to combat global warming by reducing the amount of heat the flat roof reflects back into the atmosphere, and also by soaking up carbon dioxide (used by plants to make food). Plant geeks will be interested to know that the sedums include: sedum album, sedum acre, sedum reflexum, sedum seramentosum, and sedum linare.