Green Roofs

Green roof technology is a classic case of unintended consequences especially if it is not designed properly. The green roofs can look visually pleasing and reduce storm water runoff.  However, an improperly designed green roof allows the roots of the plants to penetrate the roof membrane and allows water to infiltrate the building.  With a three to five inch rain fall event this can result in water damages from 1/4 million to a million plus in US dollars.  Retrofitting an existing roof requires an assessment of the load bearing capacity of the existing roof.  A properly designed system makes it physically impossible for the plants on the roof to contact the roof membrane.  In this darkly humorous article Seeing red over green roofs by By Joseph Lstiburek, he outlines problems and design considerations for green roof technology.  As with all new technologies it is best to learn as much about the design and maintenance of the system before installing it.  

Plant growth on a roof - an unintentional green roof  Photo -N.Carlson