According to the Roofscapes case study – see below – “This project demonstrates green roof installation methods that are appropriate for large-scale industrial/commercial buildings. This demonstration focuses on managing roof runoff to alleviate potential water quality impacts and on assisting in compliance with NPDES pollution abatement requirements. The two roof assemblies were selected to represent an optimized trade-off between minimizing weight and maximizing the absorption and filtering of rainfall. The light-weight single-media Type I: Flower Carpet system utilizes a high-performance drainage fabric manufactured by Optigr?n International AG (3″ depth). The Type III: Savannah green roof is a two-media system (4″ depth). It is expected to enhance water quantity and quality performance. Plants in both roof areas were established from Sedum cuttings and stabilized with hydro-mulch.”