Bringing the city to life with vertical and roof gardens

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Roof gardens and vertical gardens are not only aesthetically pleasing but can, if designed correctly, provide excellent functionality for temperature insulation, provision of microclimates and biodiversity benefits. They improve the physical environment by reducing glare, filtering air pollutants, recycling water. Reducing stormwater run-off and reducing the urban heat-island effect by evaporating water. In terms of urban amenity roof and wall gardens provide a more natural urban environment for city workers and deliver opportunities for gardeners to grow their own food in heavily built-up residential areas.

The installation of green walls and green roofs are becoming more popular as a means of incorporating green space into highly built-up areas. One Central Park in Broadway, The Hilton in Sydney and the Brisbane Airport link green wall are all excellent examples of green walls that SESL has helped deliver by designing and specifying high longevity and low-density soil media.

When developing soil blends for green walls and roofs one of the most important properties is the saturated density. This is the density of the soil once saturated with water which is the maximum density a soil can attain. Depending on weight restrictions of the building, the saturated bulk density should be <1.8kg/L or 1800kg/m3 and in some situations <1.3kg/L.

Therefore, it is essential that lightweight materials are used to ensure engineering requirements are met. Organic materials have lightweight properties; however, SESL recommends not using more than 30% of organic materials as they naturally slump overtime as they decompose and lose volume and air-filled pore space declines. In hard to reach spaces such as walls and roofs, it is not feasible to “top-up” the slumped media; therefore, it is preferable to use mineral components which have an unlimited life-span. Despite some slumping, it is recommended that organic matter is still incorporated at around 20 – 30% as they serve an essential role in supporting soil microbial life.

Mineral media used to maximise longevity must however be lightweight and have high porosity. Examples of lightweight mineral materials include horticultural ash, perlite, scoria, pumice and diatomaceous earth, or artificial components such as urea formaldehyde and styrofoam.

To determine if your media is suitable for use in a green roof or greenwall we strongly recommend testing to be undertaken in accordance with Australian Standard 3743: Potting Mix Non-Specialist (Regular or Premium Grade) or Specification E3: Low-density container and green roof (Leake & Haege 2014).