As garden space in Australia’s cities increasingly becomes a premium, and with concerns and awareness about global warning and the environment on the rise, installing a rooftop or green garden may well be the solution for many urbanites and landscape architects.

Infolink takes a quick look at the main benefits and considerations of installing a rooftop garden.

Are rooftop gardens and green gardens the same thing?

Not exactly. Green gardens originated in the Baltic countries, where they install live, turf roofs for their ecological benefits only. A roof garden is for recreational use as a garden space and may or may not offer the same benefits as a green roof, depending on their design.

What are the benefits of installing a rooftop garden or green roof?

There are many benefits for the property, owner and urban area that can be derived from installing a roof garden. Dependant upon the design, these include:

  • natural insulation for the building;
  • keeping internal temperatures more consistent;
  • increased cost and energy efficiency with less need for heating and cooling;
  • extends the life of the roof;
  • adds beauty to the area;
  • reduces dark, heat trapping city surfaces, helping to lower city temperatures;
  • helps to improve air quality;
  • absorbs rainfall and helps with storm water management;
  • reflection of heat and filtering of air by plants;
  • increases recreational space;
  • haven for creatures and wildlife, creating an urban habitat;
  • increase the value of the property;
  • economical and efficient roofing solution; and
  • provides calming retreat for building occupants for those with no garden access.
To put it into context, researchers from Michigan State University have calculated that if an urban area with a population of 1 million people was to use green roofing, the cities carbon footprint would be reduced by more than 55,000 tonnes, equivalent to the emissions of 10,000 vehicles.

What factors should be taken into consideration when planning a rooftop garden?

A rooftop garden can range from a simple and careful arrangement of potted plants, to an elaborate split level garden complete with water feature and cabana. Considerations include:

  • gaining any necessary permits and planning permission from local authorities;
  • calculation of the structural capacity and condition of the roof by a qualified engineer;
  • design of the garden and calculation of total weight including water retention;
  • repair and reinforcement of the roof if necessary;
  • irrigation to supplement rainfall for year round water supply;
  • drainage for excess water in heavy rainfall to prevent structural damage or plant disease caused by pooling;
  • safe access to the roof;
  • plant and growing media choice - appropriate to local climate, conditions, sunlight and rainfall; and
  • long term maintenance - plants and materials etc. should simple to maintain with access for any tools that may be needed.
What do I need to create a green roof or rooftop garden?

It depends on the style of roof garden, which at minimum will need planter boxes, growing media and plants. A quality green roof or rooftop garden will consist of a number of layers, which from the top downwards include:

  • plants
  • growing media
  • filter mat
  • drainage layer
  • insulation layer
  • root barrier
  • waterproof membrane
  • roof deck
There are a number of companies that provide the specialist materials and advice required for constructing a green roof or rooftop garden including Atlantis Water Management , Green Roof Technologies and Elmich Australia . Visit their websites for further information..