Considering the contrasting nature of substrate components,
it is desirable to find an optimum mix to obtain ideal
characteristics of a green roof media. According to factorial
design, a total of 18 different substrate mixes (Table 2)
including the controls of substrate components were
designed and their properties were evaluated (Fig. 1). The dry
bulk density was in the range of 431e741 kg/m3, respectively
for all the substrate mixes examined. The WHC were always
greater than 33.8% whereas AFP lie above 14.7%. The high
WHC is an important advantage as it enable the substrate to
store water thereby decrease runoff volume, in addition the
stored water can be available to plants during drought conditions
(Farrell et al., 2013).