|Genora's Green Roof, Jacksonville, Florida|
Anecdotally I estimate of all stormwater flowing through and then off the entire roof, about five percent is intercepted by the living roof soil media and plants.
Individually five percent of a house's roof is not much, however collectively five percent is very significant.
On Genora's roof for example, the 130 square foot living roof over the porch captures another 200 square feet of roof run off from the area above the living roof.
Quick calculations show a two inch rainfall event across 230 square feet of roof would produce about 400 gallons of stormwater.
Normally such an amount coming off asphalt shingles would carry contaminants, not only from the petroleum based asphalt shingles but also those contaminants from the urban core atmosphere.
Jacksonville has approximately 300,000 homes and residential structures, all contributing stormwater directly or indirectly to the St. Johns River and Floridan aquifer.
If 10% of the homes in Jacksonville were to install a living roof on their front or back porch there would be a total of 30,000 homes with small green roofs. If each green roof attenuated or cleaned 400 gallons of stormwater then the total amount of treated and cleaned runoff would exceed 1,200,000 gallons.
However, just think what would happen if just half of the residential structures in Jacksonville installed small green roofs like Genora's then over 6,000,000 gallons would be cleaned and attenuated before reaching our Floridan aquifer and St. Johns River.
Now consider the fact that it is estimated there are several million residential structures in Florida. If each had a small green roof like Genora's living roof then close to a billion gallons of stormwater runoff could be intercepted and cleaned before reaching our waters.
Just as the tree lady of India, Janet Yegneswaran plants one tree at a time, small green roofs could cover the urban and suburban core one roof at a time.
Genora's efforts make a strong statement of sustainability, providing us with an example and a challenge to do something ourselves to help clean our rivers, streams and waterbodies.
Green roofs don't have to be big to impact the world. Small scale green roofs carry a message of powerful intent.