Urban development alters natural hydrologic cycles. Natural soil and vegetation allow rain and snowmelt to gradually absorb into underground aquifers, but paved streets and buildings shed this water directly into our waterways.

Assuming the regions where we have installed most of our roofs average 40 inches of annual precipitation, we are able to estimate the real-time cumulative volume of rainwater fallen on roofs that we have installed since 2003.

Living roofs mimic natural hydrologic functions and help restore the health of our watersheds.

A large portion of water that falls on living roofs is retained in the soil media and then taken up by the plants from where it is returned to the atmosphere through evapotranspiration.

Conceptual Depiction of Storm Water Retention

When roof runoff does occur, it does so at a much slower rate, resulting in decreased stress on sewer systems at peak flow periods, as the following graph indicates:

Conceptual Depiction of Buffered Stormwater Runnoff

Green roofs not only retain the rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that does run off. Pollutants from commercial, industrial and residential activities that may appear insignificant at their source are transported by rain and snow melt into storm drains that flush the wastes into rivers, lakes, or marine waters. These pollutants commonly include nutrients, sediments, pathogens and toxins. In developed areas, surface runoff is increased by changes in slope due to landscaping and increasing impermeable surface area of pavement and buildings. Contaminants accumulated during dry periods are picked up by the next rainfall and quickly moved to the drainage system.

To learn more about living roofs installed by Furbish Company, click here.