The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall.
Green shed roof drainage.
Green roofs are made up of several layers typically a waterproof root barrier layer to protect the roof a drainage layer water retention mat then the growing medium and vegetation.
Step 2 waterproof the shed.
Whereas too steep means that the growing medium slides down the roof.
Make sure that the roof has a pitch that will enable drainage.
Older green roofs often used a permeable layer of rock aggregate such as scoria or gravel for drainage.
Lay it over the gravel and attach to the frame using tacks.
This improves the drainage of the green roof which helps reduce soil erosion and aerate plants.
The rock aggregate should also have a suitable ph and be low in soluble salts to ensure plant growth is not adversely affected.
The design of the different drainage layers allows for a portion of the stormwater to be retained above where the water is allowed to flow freely off of the roof.
The clay and silt content of materials used in a rock aggregate drainage layer should be 10 per cent by mass.
Green roofs can range from roof gardens with raised beds and pots to rolled out green carpets to shed roofs containing planting cells that are filled with soil or compost and planted up with low growing perennials and grasses.
This roof was towards the shallow end of the spectrum and could perhaps have been a bit steeper.
If the pitch is more than 20 degrees from horizontal you will need to take precautions so the soil in your garden does not slip.
Having proper drainage on a green roof is a critical aspect of the system.
The drainage layer has an important role to play in the total system structure of a green roof.
During a dry period the water stored can be reabsorbed by the vegetation layer above.
When saturated these layers can weigh in at more than 100kg per square metre or 20lbs per square foot.
The slope of a green shed roof needs to be a balance between being too steep or too shallow.
Make sure that the shed roof is fully waterproof.
The drainage also contributes to good aeration of the plant roots.
It buffers water and allows excess water to drain away.
Pour a layer of gravel into the frame 2 3cm deep.
Green roof solutions offers many different drainage layer options depending on system goals regarding water retention.
Step 4 build a retaining frame.
Step 3 allow for drainage.
