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Sedum sarmentosum and Sedum lineare, two common plants for green roof, were planted in two engineered media meeting FLL standards at three depths. Root characteristics of root length density, root surface area density, and root volume density were quantified. And a key hydraulic property, saturated hydraulic conductivity (Ks) values of the engineered media with and without plants were measured. The results showed that engineered media type, engineered media depth, and their interaction all have a significant impact on Sedum root traits. For the engineered media with Sedum, only engineered media type and depth had a significant effect on Ks. When the type of engineered media was the same, with the same plant used, Ks of the engineered media at a depth of 14 cm was significantly smaller than Ks of any other depth. This can be attributed to the maximum level of RSD and RVD at the 14-cm depth. The reduction in Ks of the perlite-based engineered media due to plant roots is an important finding, as plant roots clog the pore spaces and lead to poor drainage and unexpected ponding in roofs. This research provides better understanding of the interaction between plant roots and engineered media in green roofs.