It may seem counter intuitive to have a lot of extra weight on your roof. An entire layer of growing foliage absorbing rainfall -- how can that be beneficial?
The benefits are:
-lower temperatures in the summer, insulating properties in the winter
-prevents storm drain water run-off
-air purification
-provides a micro climate for plants and insects
These factors are especially important for large, asphalt covered cities that trap heat in the summer. The run off is a big issue during heavy rainfall, because the sewer system can be easily overwhelmed, and raw sewage runs right into the local waterways.
Green roof technology is highly developed in Germany. There is a long history of houses with sod on top, especially in Northern European countries, but now the interest rising, and is altogether from a modern eco-perspective.
In New York City, they are taking a serious look at the costs and long term benefits. Imagine our dense urban cities full of green roofs...
--Bibi Farber
This video was produced by the Wall Street Journal