Is Green Roof sustainable?

1. What is a Green Roof?

A green roof is also called the eco-roof or living roof. They were built on buildings for for a long time in different countries. E.g. the Chicago's City Hall building is famous of their living roofs . A green roof is a roof that has vegetation and a medium to grow the vegetation. Its costs also depend on the type of green roof installed. 

2. What are the advantages of Green Roofs?

Roof areas are a important part in urban cities surfaces. Plants on green surfaces can absorb heat and then use it through evapotranspiration. Therefore, green roofs is very important for reducing urban temperatures, and improve air pollution/smog, reduce the urban heat island effect.

Green roofs store rainwater in the plants and soil, water then be evaporated into the atmosphere. In summer, green roofs can retain rainfall from 70-80% ; in winter, they can retain from 25-40%.

Green roofs can reduce and delay run off when there is heavy and prolonged precipitation. A study in Germany stated that when there is a 10mm rainstorm, 200 litres of rainwater fell on an 18m2 green roof ,only 15 litres will run off from the roof to the ground.Therefore, it can reduce the run off on the storm water drainage system, and reduce the chance of local flooding.

Green roofs can also trap the dust in the air to reduce air pollution and has positive impact on people physical and mental health, also lower the temperate of the building.

However, it is really sustainable in all kind of roofs and situations?

3. The "sustainability" of Green Roofs

• The right kind of vegetationAccording to Scott MacIvor, from York University in Toronto, sedum does not absorb water as good as other plant species. At certain times of the year, sedum actually absorbs heat instead of reflecting it. What even worse is that it does not encourage biodiversity of plant species on the roof. According to MacIvor’s research, green roofs provide the most benefit when they are planted with a diverse group of species that are adapted to local conditions.
• The right installation
  A drain screening system is needed to prevent soil or other sediments from accumulating in your roof drains. A blockage of one or more drains due to sediment could turn your lawn into a flood disaster, and your roof will no longer be sustainable because of the cost and maintenances involved. The root penetration barrier is also needed to prevent the root growing into your house and causes leakage.

A green roof failure ecample:
vegetations struggle to grow on it

In my opinion, green roof is still a good options to improves the sustainability in the urban area. However, the installed must be well prepared or consulted by a green roof specialist. and include a wide variety of vegetation that is suitable for green roof. A regular check to maintain the green roof is also recommended. It is a sustainable tool if you use it correctly and carefully.

Reference:

"Green Roof Technology Blog." Green Roof Blog. Accessed March 23, 2016. http://www.greenrooftechnology.com/green-roof-blog/tag/maintenance_on_Green_Roofs/. 

B., Jonathan. "What Are Some Potential Green Roof Problems? - Good Question." Accessed March 23, 2016. http://www.apartmenttherapy.com/atgreen-home-re-29590. 

"European Federation of Green Roof Associations - EFB." Green Roofs. Accessed March 23, 2016. http://www.efb-greenroof.eu/verband/fachbei/fa01_englisch.html. 

Hilary, Dave. "Green Roof." EzineArticles. Accessed March 23, 2016. http://EzineArticles.com/5237712.