Green roofs have many eco benefits including; slowing of storm water runoff, wildlife habitats, aesthetic appeal and control of extreme temperature. Green or living roofs originated in Scandinavia using birch bark and turf.
There are three main types;
Extensive green roofs have a thin growing medium and are planted with sedums that retain moisture. They usually require no maintenance, except for some initial irrigation and are generally less costly to install.
Semi-intensive (semi extensive) green roofs have a greater depth of substrate to allow planting of grasses and medium size plants.
Intensive green roofs have a deep growing medium, which allows the use of trees and shrubs. Some city parks are in fact intensive green roofs and are on top of large buildings. The depth of the growing medium requires extra loading requirements within the holding structure and requires a complex irrigation system for maintenance. They are generally quite costly and require extra structural design to the building.
Expanded clay pellets are very light and allow the substrate to drain freely. It is a perfect medium for growing alpines and grasses. This is best mixed using a concrete mixer if it is a large amount.
Brown roofs usually use spoil from a local garden or building construction and are left to colonise freely to create a biodiversity habitat. The bare substrate is just left to let nature take its course. Log piles, gravel and even small pond areas. This is probably the least expensive way to create a living roof.
For my own green roof project at home, on a new extension an EPDM liner was glued to the ply board. A root barrier and membrane was then laid. I am currently experimenting with used car tyres which will hold a reservoir of moisture on a slope and create a framework to stop the soil slipping. The top of the tyre is cut out to create a container. You can make a timber grid that will stop slippage but will need a drainage layer with moisture pockets.
By Mark Tolfree of Gabriola Garden Design
Click Projects below to view details
GRFGGD001 - Green Roof Shelter Over Seating