Construction of Villanova’s Green Roof took place in 3 days in the summer of 2006. The design was a retrofit of a small portion of Villanova’s Center for Engineering Education Research (CEER) roof. The green roof is located on a second storey terrace above the “Holy Grounds” coffee shop. It is highly visible because it is located outside of the main stairwell and serves multiple purposes.
- By eliminating the first half inch of rain falling on that portion of the roof for any storm event.
- By providing research opportunities for students and possible quantification of the environmental advantages of a green roof.
- By providing a much more aesthetically appealing roof than its predecessor.
Underlying the green roof is a traditional roof which was refinished in order to ensure maximum life of the green roof. The next layer is an additional waterproofing layer which is also resistant to root penetration. On top of this layer is an insulation layer which is a thick mat designed to keep the potential for a large temperature gradient between the surface of the green roof and the original roof layer. The insulation is overlain with a geosynthetic layer that serves several purposes including drainage pathways, water storage areas, and aeration. This layer which looks much like an egg crate has holes at the high points to allow excessive amounts of water to drain. A filter fabric lies on top of it and allows water to pass through but keeps the fine sediments from the growth media from occupying the voids in the drainage layer. The media is a mixture of baked minerals which look like gravel and make it hard for weeds or anything aside from the highly specialized Sedum species to grow.
The environmental advantages that a green roof can provide are the reduction of stormwater runoff coming from the developed site. Reducing the amount of runoff that runs directly to piped systems lowers peak flows in downstream areas which can reduce erosion of the channels and the resultant sediment pollution. This site alone will not solve this problem but if similar runoff reduction systems are utilized in other developing areas, then the cumulative effects will help alleviate the situation.
In addition to preserving the environment downstream of the site, green roofs are also environmentally friendly and cost efficient to the building occupant. The green roof shields the originally sealed roof from the very intense UV radiation from the sun. The multiple layers of the green roof also act as a buffer and do not allow temperatures at the original roof surface to fluctuate drastically. These two factors can extend the life of the roof greatly. The insulating effects of the green roof can also allow the building to retain its heat in the winter and keep the radiant roof temperatures from heating the building in the summer.
The green roof is a very practical BMP in highly urbanized areas where there may not be room for an infiltration BMP in the ground. Its footprint on the landscape is no more than the building itself because it stores the water on the roof and is used by the plants or evaporates. This site should provide useful insight with respect to the actual capacity of a green roof in the field. The green roof is incorporated within the “Best Management Practice Demonstration Park” on Villanova’s campus. It adds to the list of BMPs in use on the University’s campus and will be monitored and evaluated to determine its effectiveness.
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