Substrate Loss is Minimal in Vegetated and Un-vegetated Extensive Roof Modules Over a 14-Month Period

The presence of vegetation is thought to reduce loss of soil substrate after roof installation; however, few attempts have been made to quantify this effect. Twelve green roof modules placed at a 2% slope were used to quantify the effect of wind, precipitation intensity, vegetation and vegetation type on modular green roof substrate depth. The presence of vegetation reduced substrate loss immediately after installation of equipment, yet had little effect on substrate depth once the substrate had settled. Neither wind speed nor precipitation rate had a direct effect on substrate depth, although after some large rainfall events substrate depth increased due to media expansion caused by the retained water. Overall we observed negligible substrate depth decrease, regardless of vegetation presence, wind speed or precipitation intensity.