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Feature article

A Green Roof Case Study

WORDS BY Brod Street

Key benefits of greens roofs:

  • Calming stormwater. Close to 70% of the Hawthorn neighbourhood, where this green roof is located, is comprised of hard surfaces. These generate stormwater runoff and lead to flooding, and movement of litter and contaminated water to the Yarra River and Port Phillip Bay. Roofs make up 40% of local non-pervious surfaces. This rooftop grassland can store about 5mm of rain, helping to reduce the intensity of runoff and its associated problems.
  • Cooling our home with plants. Comfort levels in the home are a major benefit. The roof cavity temperature of this home was measured to be 10 degrees lower on a hot day compared to pre-green roof days. During the January 2014 heat wave of 42; 41; 43; and 42°C consecutively, the underlying rooms did not exceed 28°C.
  • Native habitat. This green roof is one of a patchwork of habitats throughout the suburb which support native plant, insect and bird life.
  • Innovative gardening. Small terrace homes are often starved of private gardens with adequate access to the winter sun. An advantage of a semi-detached Victorian terrace dwelling is the secluded space in the valley between two sloping roofs. This is perfect for a private green roof.

Close up of the aluminium tray system. This tray has self-seeded native Knobby-Club Rush growing between the mulch of broken terracotta.

Photograph: Julie Firkin.