When designing a green roof, the components required will depend on the type of vegetation specified and how the balance between water retention and drainage is achieved to meet the demands of the vegetation and of the local rainfall levels.
The general principle is to recreate the conditions nature provides in a much shallow depth. In all green roof scenarios, substrate depths are completely dependant on the vegetation specified and the different drainage / water retention layers are selected according to the levels of water required to be held within the construction
Intensive Green Roofs
Soft &/or hard landscaping
Soft &/or hard landscaping
Drainage only for soft landscaping
|Substrate and vegetation|
|Filter layer||Filter Fleece||Filter Fleece||Filter Fleece||Filter Fleece|
|Water storage / drainage layer||DSE 40||DSE 60
|Protection mat||FSM 1100
||FSM 1100||FSM 1100||FSM 1100|
|Separation layer||PE Foil||PE Foil||PE Foil||PE Foil|
Extensive Green Roofs
XF301 sedum blanket system
Biodiverse or wildflower blanket
|Substrate and vegetation||XF301 System|
|Filter layer||Filter Fleece||Filter Fleece||Filter Fleece|
|Water storage / drainage layer||SDF Mat||DSE 40
||DSE 20||DSE 40
|FSM 600||FSM 600||Eco Mat|
|Separation layer||Not required||PE Foil||PE Foil||PE Foil|
The different vegetation options will require different depths of substrate (growing medium) in order to support the plants and their root structures. Intensive roofs require careful design considerations and the desired planting scheme will reflect that of a ground level garden or recreational space.
Pre-grown vegetation mats – will establish quickly and give high aesthetic finish immediately after installation. Available as sedum or wildflower vegetation options
Plug plants – enable a particular selection of species to be planted with establishment reached in 1+ year. They require thorough attention and maintenance as well as particular care to keep airborne seeds from germinating and forming unwanted cover on the roof.
Seed – offers a lower establishment cost but will take a couple of growing seasons to gain cover.
For an extensive green roof the vegetation options can be combined
Generally the depth of substrate is dependent on the type of vegetation being installed. Low growing sedum will need very low levels of low nutrient, free draining substrate. Wildflowers will require deeper substrate (100-150mm). Herbaceous plants, shrubs and trees on intensive green roofs will require greater depths (300-450mm+). As planting becomes more substantial it is likely to require a higher organic content within the substrate.
This layer is a polypropylene geotextile fleece that prevents substrate fines and sediment from being washed in to the water storage or drainage component. The pore size is around 0.13mm.
This layer helps to maintain the balance between the levels of water to be held on the roof to support the vegetation whilst allowing the surplus amount to drain away so that the substrate doesn't become waterlogged. The water storage cells can be filled with coarse gravel or crushed brick to increase the compressive capabilities of the build up. The components can be manufactured from a variety of materials such as high density polyethylene (HDPE) or polystyrene; each having their own reservoir capacity.
This layer delivers protection against damage to the waterproofing system that lies beneath the green roof. The layer can be of varying thicknesses, selected and specified to cope with possible levels of mechanical damage that the waterproofing could be subjected to . This is fundementally in relation to the intensity of the vegetation scheme. For example, extensive green roofs would generally experience much lower levels of mechanical damage during maintenance and therefore only require a protection mat to meet those expectations. The Bauder protection mats are manufactured from the following materials:
- Eco Mat - recycled polyester and polypropylene
- FSM 600 and FSM 1100 - polyester and polypropylene fibre mix
- Pro Mat - recycled shredded rubber
This layer ensures that the building structure and its waterproofing can move independently of the green roof so allowing for movement such as thermal expansion without shear forces created by the weight of the green roof restricting it. The Bauder separation layer, PE Foil, is a polyethylene foil manufactured from recycled granules.