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Growing a green roof at the Pittsburgh Zoo & PPG Aquarium

Construction begins on the green roof. Photo by Susan Pierce

The Green Building revolution is hot in Pittsburgh; our suddenly trendy town is breaking away as a leader in eco-friendly construction and frequently gardens are topping it all off.

 

Susan Pierce, one of three gardeners on the staff of the The Pittsburgh Zoo and PPG Aquarium, is responsible for creating and maintaining a green roof atop the Water's Edge/Polar Bear Building. Recently she talked to us about the project and explained how it came about. Sue has chronicled the whole process of building, planting and tending the green roof in photographs and she generously allowed us to show many of them here.

 

A.: I remember reading about them years ago and seeing one while visiting New York City over 20 years ago.

 

A.: The major advantage is preventing flooding and erosion from storm water runoff. The plants and media on the roof absorb from 60% up to 90% of that rain or storm water. Another benefit of green roofs is they add a layer of insulation to buildings, keeping them cooler in the summer and warmer in the winter which results in energy costs savings. They also have a temperature moderating effect in the inner city by reducing heat that is generated from roofs and buildings. Green roofs are aesthetically pleasing while softening the hardscapes in cities. They also provide habitat and food for bees, birds, butterflies and other small mammals.

 

A.: There's a two foot thick slab of concrete on the roof to support the weight of the soil and plants.

 

A.: The components were assembled in the fall of 2006 and early 2007. The plants were installed the last week of August and first week of September 2007.

 

A.: One side of the roof is referred to as an intensive green roof. The other side is an extensive green roof. They differ in the soil depth as the intensive side measures from 4” to 3’ deep, whereas the extensive side is consistently 3” to 4” deep. The soil composition of each side differs in their mineral and organic components. The intensive side is basically a rooftop garden with small trees, shrubs and perennials. This side needs to be irrigated at least once a week in the summer and sometimes twice a week when rainfall is scarce. The extensive side is planted with very drought tolerant perennials that can withstand the shallow soil depth and lack of moisture. The extensive side was only irrigated for 3 weeks after planting and then it was left to adapt to dry, hot, windy and cold conditions. We also planted the extensive side with 14 research plots where we are recording various data, i.e. plant growth and performance. We chose some plants that we think have not been tried on green roofs yet.

A: The soil was brought in January 2007. A truck containing the soil was parked on the road in Highland Park, above the Aquarium. The soil was blown down to the roof through a large corrugated plastic tube. I believe that took a few days. We had to wait until construction of the building was completed before we could plant the roof. Then in late August 2007, we had to rake the soil to make it level on the extensive green roof side. We had to move soil and mound up soil to about 3’ deep on the intensive side to accommodate some small trees and shrubs that were to be planted there. It was challenging to bring all the trees, shrubs and plants up to the roof with only one standard door for access. Many of the trees and larger plants were dropped off at the Water’s Edge/ Polar Bear building’s loading dock. We transported them on flat carts up a service elevator to the roof level and then had to squeeze them, usually by hand, through the doorway to the roof. Needless to say it was very difficult and being August it was very hot. It took about 2 weeks to plant the roof. Even though the roof was planted during some very hot days (90’s) in August, which is contrary to most horticultural guidelines, most of the plants survived the first year.

 

Sue's description of the exhausting work sounds daunting even to those of us familiar with the back achingly hard side of gardening. The efforts that she and the other zoo staff put into the Green Roof have produced glorious results and in the next Pittsburgh Gardening Examiner article, we'll tell you more about what Sue planted, how it worked out and how you can catch a glimpse of the Zoo's Green Roof.