What’s a green roof?
A green roof/ living roof is a vegetated landscape system installed on a roof or building structure.
Green roof at the Adelaide Sustainability Centre
We installed a green roof not only for its environmental benefits, but also so our community can visit the demonstration site, learn about green roofs, and be better supported to install their own.
We wanted to retrofit our shipping container onsite, which was suitable as they are waterproof and a structurally strong frame. We were inspired to implement the project by Aldinga residents/community educators, Sam and Dani, who had installed a green roof on their own shipping container and shared their process (read more in resources below).
The project was seeded by Green Adelaide.
What’s so great about green roofs?
The benefits of green roofs include:
- Reduced stormwater run-off – By installing the green roof onto the impervious shipping container roof, the permeable surface area is increased, and stormwater runoff is slowed and reduced.
- Utilisation of stormwater – Rainwater is used to support the green roof’s living vegetation, reducing the stormwater running off of hard surfaces and into our drains. Additionally, excess water filters through the drain system and into a rainwater tank where it can be reused.
- Urban cooling – Green roofs mitigate the impact of the urban heat island effect, and in our case, it reduces the temperature of the previously exposed shipping container roof and surrounding area
- Improved thermal insulation – As a permeable surface, green roofs regulate the temperature of the host infrastructure, reducing heating and cooling requirements
- Increased urban green spaces and wildlife – Green roofs provide urban vegetation and habitat to attract invertebrates and birds
- Improved stormwater run-off quality – Stormwater pollutants are filtered and excess water can be reused for non-potable use
- Improved air quality – Green roofs clean the air by lowering temperatures, removing pollutants from the air, and preventing additional air pollution (associated with heating and cooling buildings).
The green roof and other environmental and sustainability resources and displays are available to visit at the Adelaide Sustainability Centre on Mondays, Tuesdays and Friday 10am-3pm.
How is a green roof constructed?
Green roofs consist of a series of layers including waterproofing, drainage, filter fabric, growing medium and vegetation.
Before beginning construction, we had an engineer approve the builder’s design, to ensure that the shipping container would properly support the weight of the green roof structure, saturated soil, plants and people on top of the roof for maintenance purposes. Our green roof was designed for 300mm saturated soil cover.
The builder constructed a timber frame on a 3 degree slope, in order to enable drainage of additional water. This frame was fixed to the shipping container roof, with a plywood container box built on top to contain the green roof. The structure was offset to the north, to overhang and cover the accessible side of the shipping container and the powerpoint, and to allow for a drainage hole.
The waterproof layer was then installed on top of the ply and up the sides of the box, with thick pond liner we had on hand. As we did not have a single sheet large enough to cover the box, it was joined using silicone, waterproof tape and sealed using bitumen paint. A hole was cut on the north-west side of the box, through the waterproofing layer. A 90mm polypipe was connected and sealed to the membrance with silicone and bitumen paint, to avoid leakage. PVC pipe guides excess water from the box into rainwater tanks below where it can be reused.
Above the waterproofing layer is a drainage layer made from recycled plastic sheeting called Hydrocell. The panels interlock and form a 30mm gap between the waterproofing and soil layer, so excess water can drain.
A permeable fabric layer is installed between the drainage and soil layers, to prevent the substrate from washing away, we used a geotextile from Global Synthetics. This permeable layer enables water to flow through, but prevents soil particles and roots from penetrating it.
As outlined by Sam and Dani, the depth of growing substrate can range from 100-1000mm depending on the type of plants the green roof will support. We opted for around 230mm of soil, anticipating it would settle to a reduced depth. We used a sand, loam, compost blend from Adami’s and were fortunate to have their assistance emptying the over 3 tonnes worth of soil from bulka bags onto the roof with a crane, saving us a lot of manual labour.
Following the substrate layer, we installed drip irrigation, primarily to support the plants during the first Summer. We included a system flush in the irrigation on the north-east corner, enabling us to flush any soil particles from the irrigation when needed.
We selected 50 plants, 10 different species of native grasses, sedges and groundcovers from State Flora (see our plant table below). We considered growth size and type when planting, in the hope that some plants, such as Karkalla, Creeping Saltbush and Hardenbergia, will overhang on the northern side once they have established.
We predict the green roof to require occasional irrigation, particularly in the first Summer after installation, weeding a couple of times a year, and potential additional plantings.
What suppliers did we use?
We used the following providers:
G.W. Wittmann & Assoc. structural engineers 08 8352 776
Schebella Carpentry Ben.email@example.com 0477 707 150
Adami’s San and Metal Depot adamis.com.au/
State Flora stateflora.sa.gov.au/home
Global Synthetics globalsynthetics.com.au/
This project was made possible by Green Adelaide funding. Advice and the below article from Sam and Dani was really useful in assisting the project.
Where can you find out more?
Visit Water Sensitive SA’s interactive map to find out more about other green roofs and water sensitive urban design projects in South Australia.