The word Green Roof has come to describe a roof which is green in the economic sense.  In other words it is energy efficient or sustainable.  It has many different names such as a living roof, biodiverse roof, Sedum roof, brown roof, eco-roof, grass roof, turfed roof, etc. Basically, it is a living roof which is placed on a building instead of a conventional roof. There are various components that are necessary plus the main structure of the building must be tested before any attempt to put a green roof onto a large expanse of roof. There are many benefits surrounding green roofs including, helping to control water in areas of flash flooding as it absorbs more water slowing the release of rainwater.  It can be used as a filtration method capturing the run off water and using it for other uses such as brown water (flushing toilets etc). Experiments have shown that a green roof such as a Sedum Roof can help both with insulation during colder months and a cooling effect during hotter times. One of the main and most popular reasons for having a green roof is that they increase the biodiversity of wildlife including insects and birdlife.  This makes it much more attractive to look at than a conventional roof. A green roof will also filter pollutants in the atmosphere especially carbon dioxide, lowering the carbon footprint but also helping lower disease rates such as asthma.

If all the roofs in London had green roofs the air would be far cleaner.