This column, if you will, is a post for issues specific to the green roof industry.  You might find some of the topics divergent if you are familiar with other Green Roof industry blogs.  We believe this is because the content comes from developments in the Midwestern construction market, namely Chicago.

The building practice of covering a roof with living, eco-roof systems is new to the United States–less than 10 years as a specified construction practice for commercial and municipal buildings.

However, the city of Chicago, led by its mayor, has adopted a goal of addressing a source of fresh water pollution threatening its residents by embracing several measures of Low Impact Development. The sewer systems of Chicago–like those of over 700 other communities in the U.S.–combine the flow of storm water runoff with our daily sewage.  Unfortunately, waste treatment facilities are not able to digest volumes of combined sewer overflow (CSO’s) during significant storm events.  Facilities for waste treatment must manage this flow by diverting the diluted but still untreated flow directly into our streams, rivers and lakes until the surge has passed.  Only then can waste treatment begin again.

The communities affected by CSO’s are the areas of the country closest to the Ohio River and Mississippi River Valleys, two of our largest fresh water river systems.  These river systems drain an area of 1,151,000 square miles.  The highest geographic concentration of communities that experience excess CSO’s are those with the oldest sewer systems, naturally, and they are located in the eastern part of this drainage basin.  See more data on the National Pollutant Discharge System site from the EPA.

An approach for remedying this problem is to cover 40% of all new construction (as mandated by the City of Chicago) with effective storm water detention systems.  One method of detaining these flows is with mature vegetated green roofing.  Namely, Extensive type: shallow profile media and plantings that will absorb most events and detain the flow of water until the surge of the storm has passed.  Most of the precipitation during these events can then evaporate back into the atmosphere.  These systems can detain the statistical 1 and 2 standard deviation events in the geographical area of concern.  The widespread use of storm water detention systems will take pressure off our waste water treatment infrastructure, and, allow more effective treatment of water before it is returned to the environment.

These postings will continue to investigate issues of effective construction, trade practices, scope of construction issues, manufacturer concerns, and legislative issues arising from this and other sustainable building trends that include green roofing systems.  I hope to develop a volume of material from the collaboration of professionals in the industry and encourage all of you to weigh in with controversy.

Regards,

Kate