The term "green infrastructure" refers to a strategic network of vegetated areas and water retention techniques intended to mitigate stormwater problems. Examples include greenways, rain gardens, green roofs and rain barrels. Often, green infrastructure can cost less to install and maintain than traditional, "grey" infrastructure and provide additional benefits to the community, such as green space.
Like many older cities, Pittsburgh has a combined storm and sanitary sewer system, which means wastewater from homes and businesses flows through the same pipes as stormwater to a water treatment plant. During wet weather events, the extra stormwater in the pipes can cause them to overflow, spilling untreated sewage into rivers and creeks, creating a "combined sewer overflow" (CSO). In fact, as little as 1/10th of an inch of rain can cause a CSO!
The amount of impermeable surfaces, like roadways, roofs and parking lots, also contributes to stormwater problems because precipitation cannot slowly seep into the ground, but rather washes off into storm drains.
Green roofs are planted over existing roof structures, and consist of a waterproof, root-safe membrane that is covered by a drainage system, lightweight growing medium and plants. In addition to their stormwater benefits, green roofs can last twice as long as traditional roofs and can insulate buildings to reduce energy costs.
To find out more information about green roofs in Pittsburgh, visit http://www.greenroofs.com/projects/plist.php.