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*Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around 50% <ref name=VS/><ref name=Hill/>.
*Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around 50% <ref name=VS/><ref name=Hill/>.
*Using a compost based planting medium improves retention by around 10% (i.e., 60% for compost compared to 50% for granular).
*Using a compost based planting medium improves retention by around 10% (i.e., 60% for compost compared to 50% for granular).
*Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modeled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.
*Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.
An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>Curve Number and Runoff Coefficients for Extensive Living Roofs
An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>Curve Number and Runoff Coefficients for Extensive Living Roofs