Side-by-side comparison of green roofs compared to white roofs at one Chicago Walmart
(2013) Cooperative effort by WalMart, Green Roofs for Good, Green It, Penn State, Environment Canada and Arup. This report summarizes the findings of the Walmart green roof performance evaluation project. This work centered on a purpose-built research roof that was constructed in 2006 at Walmart store #5402 at 4650 West North Avenue in Chicago, IL. The 133,000 sq. foot roof is just over half green (vegetated) and just under half white, “cool” roof. When constructed, this roof was the largest, most intensively monitored green roof in the world. For growing season rain events less than one inch (90% of the rain events recorded) the roof retained an average of 87% of the precipitation. For larger events (up to a daily maximum of 3.63”) the roof typically retained 58-61% of the precipitation. The green roof reduces peak heat load compared to the white roof, but the green roof’s overall impact on summer heat flux is similar to that of the white roof. Complete details of the project, monitoring parameters, results and discussion are provided in this 45-page pdf document.