Drainage layer Roofdrain 20 acts as a water reservoir holding an additional 5.3 litres of water per square metre to further reduce the runoff from the roof. This stored water can be released slowly, used as grey water or even used as irrigation for the vegetation mat.

Roofdrain, is a green roof drainage and water storage layer consisting of a High Density Polyethylene Properties (HDPE) core laminated to a geotextile filter. It can be used on horizontal surfaces and sloping roofs. On sloping roofs the available storage capacity within the Roofdrain core will be less than that available when laid horizontally.

The core acts as a water reservoir holding 4.5-5.5 litres per square metre for plants to access in dry periods. The core is perforated to allow excess rainwater to flow into the underside and away to drainage outlets. The upper geotextile prevents any fine particls from the substrate blocking the drainage layer and has a zero breakthrough head to prevent over-saturation of the substrate. The lower textile is a fleece layer that protects the waterproof membrane. The protective fleece also acts as an extra moisture retentive layer, holding an additional 1.0 litres per square metre to further enhance the storm water attenuation benefits of the system.

The table below shows the available storage capacity at a range of inclinations. Typically Roofdrain is used in conjunction with a textile covering or soil which will provide additional storage capacity.

This is the bare core storage capacity; other elements of the system can be expected to provide additional storage.