Comparisons of extensive green roof media in Southern Ontario

Thirty-three extensive green roofs in southern Ontario were surveyed and samples of planting media recovered for hydrological laboratory analyses. The resulting data demonstrate a significant dominance of the role of organic matter in the physical and chemical properties of the media. This is very apparent owing to the local practice of basing some green roof media on composted materials rather than on the European recommendations of lightweight minerals or aggregates. The desirable characteristics of increased maximum water holding capacity and lower bulk density are both well correlated to the percentage of organic matter found in the media samples. Within the roofs surveyed, the percentage of organic matter, even in association with increasing maturation, was not a significant indicator for loss of green roof planting depth. Particle size distribution (PSD) parameters were also measured and compared to the water transport properties of the media (permeability and maximum water holding capacity).