Topic 1
Recall that a green roof is a specially engineered rooftop that supports vegetation and plant life to the benefit of the environment.
Among others, it can reduce air pollution, mitigate against urban heat, act as filter for rainwater and reduce energy demands…
What are however the building elements or components of green roofs?
There are several components that make up a green roof system (Dinsdale, Pearen & Wilson 2006):
Waterproofing of the roof deck
Root barrier
Drainage Membrane
Filter layer/geotextile filter
Green Roof Substrate/growing medium
Vegetation
Many roof decks already have a waterproof layer (can be anything from bitumen membrane or coating, asphalt on a shed, or some form of liquid waterproofing).
In case of no waterproofing layer, you should add one.
For bigger projects (i.e., intensive roofs), you should add a stronger waterproofing compound.
- You can include a root barrier above the primary waterproofing layer to prevent any roots causing damage to the structure.
- These can be thin polyethylene plastic membranes that can be laid across the waterproofing layer and joined with tape.
- In intensive roofs, root barriers are essential due to vigorous roots of the vegetation.
- The drainage system deals with rain and storm water.
- Usually, it is an HDPE membrane, which features cavities/cups that retain water until it is required, when it is drawn back up by the vegetation.
- Any excess water (e.g., heavy rain) passes through perforations and then travels through to a drainage space where it can be safely evacuated via a drainage outlet.
- A good drainage membrane is of high-quality HDPE plastic, has high compression strength, it is lightweight and easy to install.
- Vegetation needs a regular water supply as well as nutrients.
- This often relies on drip irrigation system that provides water and nutrients under the surface.
- Under the surface irrigation systems are more efficient that sprinkler systems.
The filter layer on a green roof is designed to prevent soil and other substrates, as well as debris, from filling the cavities of the drainage membrane.
- These can be specially designed, being a custom blend of aggregate and organic materials based on your needs.
- These can include bricks and aggregates, compost, medium clay soils and even volcanic rocks.
- For extensive roofs, suggested vegetation include mat-forming species of Sedum, Sempervivum and moss. Ferns such as Polypodium vulgare and Asplenium trichomanes are suitable for dry shady conditions.
- For semi-extensive roofs, suggested vegetation include dry habitat perennials and ornamental grasses such as rudbeckia, achillea, potentilla, armeria, dianthus, helictotrichon sempervirens, stipa tenuissima. (this topic has been analysed in Module 4)
- For intensive roofs, suggested vegetation include drought tolerant plants that are both sun and wind tolerant.
