Extensive Green Roofs
_Extensive Green Roofs And Wildlife Gardening
Extensive Green Roofs are the most effective method to establish a Sedum Roof in an average sized urban wildlife friendly garden.
Once we have the roof established with the lightweight growing medium we are best considering using drought tolerant plants, these can range from grasses to wildflowers and often includes the well tried and tested sedums.
There are stages that are very important to adhere to
so as not to experience any future disappointment.
One obvious and vital factor is to make sure the roof is and remains watertight. This starts with the actual structure itself. The more firm and flat the surface is, no matter what angle the roof is, the better. It needs to be rigid.
In many ways what is being created here could be described as a very shallow pond. Just as we can use an EPDM rubber sheet liner to create a pond this method can be put to good effect when sealing the roof.
The watertight membrane needs to span the whole area and needs to be resistant to any invasive roots from the plants.
Drainage has to be considered to ensure a healthy soil structure for the plants used. Good drainage also prevents excessive weight caused by a build up of water.
A shallow reservoir of water
This feature can be made by using a pre-made structure usually plastic that resemble the structure of egg boxes, these may be in modular form or with the more flexible types in a roll.
One other alternative is to use a lightweight substrate such as expanded clay pellets which have water retention qualities.
The drainage medium only needs to be 20mm deep. An overflow arrangement into a gutter that can then be connected to a water butt or something similar to preserve water is a good idea.
Weed Control Fabric
An absorbent barrier or filter layer will be needed.
Some form of weed control fabric can be used in DIY circumstances as long as the area is not too large.
A manufactured Fleece is often used to achieve this.
In each case it's worth placing an added protective sheet between these and the drainage medium. This needs to be laid on top of the drainage layer to act as a barrier between it and the growing medium.
This avoids any loss of soil and the chance of it dissolving into
a sludge which would not only restrict growth but detract from the overall attractiveness of the roof.
Expanded Clay Pellets As The Substrate
Various companies have their own mix that achieves the desired effect which is to be lightweight and still provide the nutrients that the chosen plants can thrive on.
Home mixed substrate can be bulked out with LECA - Light Expanded Clay Granules, and if possible, also using a water retentive soil or compost will help.
For extensive green roofs, and depending on what plants have been decided on, the soil needs to be between 70 - 100mm deep, this helps provide anchorage for the plants and if any less they will be stressed during dry periods.
A Sedum Roof As The Vegetive Layer
Now the Vegetative Layer, in other words the plants.
As mentioned before for smaller structures the usual course to take is to establish a sedum roof which does look impressive when fully matured and where there is full coverage of the roof.
One drawback is it can look patchy if the sedums don't root, so it's good to have a supportive plan in mind to ensure success.
This can be as simple as having sedum seeds ready to seed any bare areas or another option is to use a mixture of shorter grasses, also herbs and where possible wildflowers to complement the sedums.
Combined with this planting strategy it's a good idea to place low piles of stones and rocks along with a few small logs in strategic or random places, this could be where any patchy spots develop.
Doing this will encourage smaller invertebrates to move in. The idea is to mirror the habitat that the local wildlife feels at home in, do that and they will take up residence.