Drainage Layers for Green Roofs

Every vegetated green roof needs a reservoir function to store water for irrigation purposes during extended dry periods  but also good drainage. Poor drainage provision can risk waterlogging of the substrate layer with consequent root damage and potential failure of the vegetation. A good green roof system will provide this at different layers within the roof make up, one of which is within the drainage layers.

The drainage layers on a vegetated green roof will typically consist of a protection fleece, unless the roof is of an inverted design,  drainage and reservoir board and filter layer. With regard to the drainage and reservoir board this will typically be manufactured from a recycled plastic and it’s important that it has good reservoir function on its upper face with individual storage cells or chambers with overflow provision so that excess water can drain away below the board. The underside of the board should facilitate good drainage so that water cannot back up through the board and risk waterlogging of the substrate layer above. For example, at Optigrun we have different drainage and reservoir boards within our systems ranging from 20mm to 60mm in depth with different performance characteristics so that the correct product can be chosen for each project. The filter fleece that’s laid above it should  have good mechanical filtration properties but also allow a sufficient rate of water flow. The current Green Roof Organisation GRO Green Roof Code (2021) sets out minimum performance characteristics for this layer.

Optigrun FKD Drainage boards are available in various designs and are selected according to which drainage target is to be achieved, either by delaying the flow, retaining water or targeted drainage of roof areas.

100 % HDPE recycling regenerate, low own weight, easy construction with high drainage capacity, safe and targeted drainage of excess water, depending on the design with and without water reservoir, for roofs with and without incline, recyclable