Green roofs are made up of several layers, including waterproofing, a protective layer, drainage layers and planting. Once rainfall has irrigated the planting, it drains away naturally through the subsequent layers.
Blue roofs are designed to capture rainwater and store it temporarily to be released later under pre-determined conditions.
Blue roofs can be combined with green systems and typically installed to replace the conventional green roof drainage layer. This type of system may contain a series of water collection units or pipes within the drainage layer.