Vertical drainage is still needed from a green roof. They are excellent at storing rainwater. They are one of the first source control mechanisms in the SUDS train... in most rain events green roofs designed using our guide can hold nearly 60% of the average rain that falls on a roof. More importantly in intense storms they significantly reduce the RATE the water leaves the roof. So green roofs play an important role in delivering green infrastructure and ecosystem services in Urban areas.
Lateral drainage across a green is always a concern on a green roof. The various ways of draining laterally are dealt with in detail in the members section of the guide.
Vertically draining a green roof
But what happens to the rain that is not stored on the roof. Where does it go and how? Here John talks through the various options covered in the guide…
Simple Vertical Drainage – where the water just runs off the roof like on a normal shed.
Boring Vertical drainage – plastic guttering and piping, which is the conventional approach.
Funky Vertical Drainage – rain chains that can go to a water butt or a conventional drain. Or even better to a rain garden and perhaps eventually to a pond.
Of course we favour the funky as it cuts out the plastic. And there are some great sites out their set up by rain chain obsessives. We go for the simple chain effect but their are some great designs out there.
Fun with rain chains
He also highlights the wider benefits of using rain chains, for biodiversity (believe it our not) though I am not sure what John is on about when he talks about using rain chains as a weapon!!!
Furthermore the rain chain effect is pretty cool architecturally as can be seen in a house extension built in Surrey using the guide.