green roof stormwater bmp

Green Roofs as a Stormwater Best Management Practice

Green roofs are emerging as an effective technology for stormwater management and sustainable building in the United States. The vegetation and planting media capture rainfall and slowly release it to the atmosphere through evapotranspiration

Green roofs have been proven to evapotranspirate the majority of smaller rainfall events (typically one inch or less) at the source.

In addition, green roofs have a longer life-span than standard roofs because they are protected from ultraviolet radiation and the extreme fluctuations in temperature that cause roof membranes to deteriorate. Vegetation helps cool the membrane and the building during the summer as the plants and growing substrate act as an insulation layer, they shade the roof.

Green roofs are typically engineered to be either extensive or intensive.


  • Relatively light (15-50 pounds/ square inch)
  • Relatively shallow growing medium



  • Heavy (80-150 pounds/square inch)
  • 12” + growing medium


Regardless of type, properly designed and maintained green roofs can deliver these ecological benefits:

  • Conserve energy by moderating roof temperature
  • Reduce storm runoff volume and peak flow rate
  • Restore urban ecology and aesthetics
  • Reduce the urban heat island effect
  • Protect conventional roofing systems, potentially doubling the life of waterproofing membranes


Does a green roof require irrigation?installing irrigation on a green roof

Irrigation is typically needed during the grow-in phase of green roof vegetation. Supplemental irrigation is usually necessary during the hottest part of the summer. Irrigation systems for green roofs must be carefully designed, installed and maintained, as excessive watering can trigger serious damage.


If you are interested in a green roof as a retrofit for your commercial property or to include in a new development, please contact us at Water in Motion. We can get you started with a feasibility study.