Assemblies

Type I - 3.00 inches of media (Roofrug®)

The PVC waterproofing is uniform across this 144,000 square foot roof, but exactly half of the roof is covered with a Roofrug® assembly. The remaining roof area is a white Energy Star® membrane roof. As a service to the city of Chicago, Wal-Mart voluntarily monitored the performance of the green roof. The roof drainage system was purpose-built to separate runoff from the green and non-green roof areas and enable precise comparisons to be made between the two roof areas. Flow meters, installed in each manhole, record total flows and flow rates from each roof section. The entire roof is outfitted with a weather station and data logger to measure temperature, solar radiation, humidity, rain, and wind speed and direction to monitor the conditions on both the vegetated roof and the white Energy Star® rated membrane. Additionally, a moisture probe was installed in the green roof media. The study was the largest and most intensive of its kind in the world. The findings from the study were first made public in Vancouver at the 2011 CitiesAlive conference.

Improvements in the rate and volume of runoff were apparent as soon as the green roof was installed. Because of the study we now have conclusive evidence that the size of a green roof affects its performance. The scale of a green roof allows it to operate at or above its expected performance rate. This benefit also relies on the non-modular design in which moisture slowly migrates through the green roof toward the outlet. Longer ‘residence times’ in the green roof result in greater moisture uptake, delayed runoff, and enhanced growing conditions for the foliage plants. The larger the green roof the greater the distance runoff needs to travel to reach the roof drains thereby further delaying the peak rate of runoff. There is no other BMP that more closely matches pre-development conditions than a large scale green roof.

A decrease in the temperature of the greened roof was also observed, compared to the adjacent white roof.

The Roofrug® is four-inches thick, contains 3 inches of media, and has a maximum weight, when saturated, of 20 pounds per square foot. The plant cover consists primarily of flowering succulent plants called Sedum. Interestingly, Store #5402 is an excellent example of a green roof established entirely from Sedum cuttings and seed. A unique feature of the Roofrug® is the incorporation of a one-inch thick foundation layer that is, at once: (1) a protection layer, (2) a drainage layer, and (3) a root supporting structure. This mat is manufactured entirely from post-industrial products. The layout includes paved walkways to access roof top utility units.

The Roofrug® is designed to be compatible with electric methods of leak detection. Due to its thin profile and its unique foundation mat, it is very easy to remove portions of the cover to examine the underlying roofing materials, should this become necessary.