THE THERMAL PERFORMANCE AND LIFE CYCLE ASSESSMENT OF A GREEN ROOF IN PITTSBURGH, PENNSYLVANIA
A green roof, a roof with a vegetative cover, is one passive technique that can be used to address environmental issues in an urban setting. Research has shown that green roofs can be used to mitigate numerous urban problems such as storm water runoff and the urban heat island effect. Green roofs can also increase the life span of roofing materials. By adding additional layers to the roof, the performance of a rooftop can be greatly enhanced.
A 12,300 square foot extensive green roof was constructed at a commercial site in Pittsburgh. A conventional gravel ballasted roof covers the remainder of the building. The green roof consists of a drainage layer, 5.5 inch thick layer of soil substrate, and vegetation. Using the conventional roof as a control, a monitoring system measured performance parameters of temperature, net radiation, relative humidity, wind speed, and wind direction.
The data results clearly show the effect the respective roof coverings have on the roof membranes. The gravel ballast covering the membrane on the control roof cannot protect the membrane from ambient conditions or radiation. The green roof works effectively during the summer and fall, when the high ambient temperature is greater than 65°F and high incident solar radiation is greater than 400 W*m-2 net. For example, on August 25, 2006 the ambient high was 90°F, the low 70°F. The control roof membrane reached an afternoon high temperature of 130°F and a low temperature of 65°F. Meanwhile, on that same day at the green roof membrane high temperature was 86°F and 73°F at night. While the green roof outperformed the conventional roof during the summer and fall, during the winter they perform equally.
An Environmental Life Cycle Assessment was also used to determine the effect of roof type on the overall environment. A conventional, extensive green, and intensive green roof were modeled. The extensive green roof impact was roughly 50% less than the control roof in a variety of environmental damage categories. The intensive green roof actually varied with each damage category, from 10% to 44%. Still, green roofs were the environmental preferable choice.
Advisor:Dr. Robert Ries; Dr. Ronald Neufeld; Dr. David Dzombak
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Keywords:civil and environmental engineering
Date of Publication:09/25/2007