As part of Green Building Week we profiled ‘The Mangrove Home’ which uses a green roof for sustainable and aesthetic purposes.  We asked our civil engineer, Ropru Rangsivek to provide more information about the topic.

Reduction of stormwater runoff

For standard housing, rainwater runs off the roof into stormwater pipes.  With large scale developments within the CBD control of this runoff water is crucial to minimise any disruption to traffic flow or pedestrians due to a build-up of stormwater.  A green roof increases the storage of rainwater which is shown in the table below.  For the Mangrove House, this meant that there was a significant reduction of stormwater going into the waterway.

Figure 1: Reduction of stormwater runoff from a green roof as compared with a conventional flat roof Schmidt, M (2009) “Rainwater Harvesting for Mitigating Local and Global Warning” in Fifth Urban Research Symposium Berlin

Figure 1: Reduction of stormwater runoff from a green roof as compared with a conventional flat roof (Marco Schmidt, 2005)

Mitigation of urban heat island effect

Another advantage of a green roof is mitigating the “urban heat island effect”.  This is where the temperature of the urban area is higher than surrounding rural areas where there is more green space.  Anyone who has visited Downtown Los Angeles during the summer months would be able to attest to urban heat island effect.  The plants convert the sunlight into chemical energy that is later used to fuel the plants (photosynthesis) which gives out a cooling effect to the surrounding environment.  Marco Schmidt et al. (2005) looked at greening urban areas by means of partially green pavements, green roofs and green façades. Their study showed that this “greening” results in cooling the urban microclimate, with the cooling rates of 302kWh/m2.a  equivalent (Picture 2).

Figure 2: Radiation balance of a black asphalt roof as an example for urban radiation changes (Schmidt, 2005)

In addition to stormwater mitigation and reducing the urban heat island effect, green roofs also purify the air and encourage biodiversity. 

Contact our civil team if you want to see what options are available for your next project.

Schmidt, M (2009) “Rainwater Harvesting for Mitigating Local and Global Warning” in Fifth Urban Research Symposium Berlin