The Chicago Walmart utilized the Roofmeadow Type I: Roofrug®. The Roofrug® is four-inches thick and has a maximum weight, when saturated, of 20 pounds per square foot. The plant cover consists primarily of flowering succulent Sedum plants. 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 recycled post-consumer products, most notably athletic shoes. The layout includes paved walkways to access roof top utility units. Plant establishment was from Sedum cuttings and seed. Depending on weather conditions, the roof should take between 12 to 18 months to produce a dense and uniform foliage cover. During this time it will be maintained by a Roofscapes, Inc. Network company. The green roof is unirrigated.

Improvements in the rate and volume of runoff were apparent as soon as the green roof was installed. A dramatic decrease in the temperature of the “greened” roof was also observed. As a service to the City of Chicago, Walmart is voluntarily monitoring the performance of its new green roof. Walmart is comparing the green roof to the exposed Energy Star roof that covers the other half of the building. The data collected from the green roof and the Energy Star control roof will include: Runoff rates and volumes; Energy flow across the roof, both into and out of the building; Roof top temperature.

These characteristics will be correlated to site variables, such as potential evapotranspiration and solar radiation, that are also being measured at the facility. This information gathered from this monitoring program will constitute the most complete database on a full-scale green roof in North America. At 74,000 sf, it is currently as of 2006 the largest green roof being monitored anywhere in the world. The Roofrug® green roof is designed to be compatible with electric methods of lead 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.