SUSTAINABLE  CANBERRA                                           australian institute of landscape architects   AILA®

GUIDELINES

GREEN ROOF

Planning

When considering a green roof consider the aims of the project.  Are you planning a green roof for:

  • Biodiversity/habitat/wildlife corridor
  • Water capture and reuse
  • Improved building environmental performance
  • Recreation/ Increase open space
  • Aesthetics/Visual appearance/psychological benefits
  • Food production

Aim to include a combination of goals, don’t just choose a green roof for aesthetic reasons only.

Getting Professional Advice

  • Seek the services of a landscape architect who can help with the planning, design and implementation of the project.  They can also advise on other professionals that may need to be involved in the project.
  • Involve an engineer early on in the project to see how an existing roof can be reinforced to support a green roof or the building detail of a proposed building. 

Types of green roof system: extensive and intensive

Extensive System

  • Shallow soil profile – eg 50mm- 300mm
  • Weigh between 45 – 170 kg/m2
  • Typically planted with low growing plants such as succulents, in particular Sedum species and drought tolerant grasses.  In more humid climates mosses are grown but these are not appropriate for Canberra conditions.
  • Not usually accessible
  • Planted for environmental and economic benefits
  • Basic irrigation is recommended for prolonged dry periods
  • Require minimal maintenance once established

Intensive System

  • Deeper soil profile – 300mm +
  • Heavier than extensive system –
  • Can be planted with a greater structural diversity of plants, including low growing plants, shrubs and trees.
  • Require more maintenance than extensive systems

Green roof profile

Typically green roofs are made up a series of layers:

  1. waterproof layer
  2. drainage layer
  3. geotextile fabric (there may be one or more layers)
  4. soil layer (specially formulated)
  5. plants

Landscape Design

Water use

  • Aim to be sustainable in water use.  Harvest stormwater and reuse for irrigation.  Where appropriate use grey water technology.  These measures will have a marked benefit to the local catchment.

Landscape Materials

  • Soil profile to include free draining sand-like product, clay minerals
  • Incorporate sustainable landscape materials wherever possible.  This will reduce the ecological footprint of the project.  Consider a specially formulated growing medium which includes a recycled component such as crushed brick which is available locally.
  • Use light coloured wind resistant landscape mulches to help reduce soil temperatures and reduce evaporation from soils.  Examples include light coloured 10mm gravel

Site Ecology

  • If practical and if original soils have not been adversely affected aim to restore some of the existing ecology to the site – this will improve site biodiversity.  If possible link site to existing open spaces and reserves to create habitat corridors. 

Choosing plants

  • On green roofs, plants will be subjected to more extreme conditions than those in a garden bed at ground level.  They will be subjected to higher temperatures, windier conditions, leading to rapid water loss and frosts during the cooler months.  Therefore plants need to be chosen well. 

Maintenance

  • Ensure a Landscape Management Plan is in place to protect investment in the green roof/wall technology.  Maintenance and replanting are vital in maintaining healthy green roofs.

Monitoring

  • Include a proportion of the budget for weather station monitoring equipment

Case Studies

   Keyakizaza Complex, Roppongi, Tokyo

References

Johnson, Chris  (2003) Greening Sydney – landscaping the urban fabric. Government Architect Publications: Sydney.

Dunnett, Nigel and Kingsbury, Noel  (2004) Planting green roofs and living walls.  Timber Press.

 

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