1) Greener skyline
2) Visual relief from urban environments
“Plants can add visual interest to plain walls and roofs and soften the ‘straight
edged’ features of industrial and commercial properties.” (Liesecke et al., 1989).
3) Enhance architectural designs, create iconic landmarks in the city
“A layer of plants can enhance good design or disguise bad design’ in building
Developments.” (Johnston & Newton, 1996).
4) Screen and isolate views (green walls)
5) Enhancing public areas
1.) Reduction of the Urban Heat Island effect and regulating of the micro-climate
- Roof surface temperature can be heated to a high of 58ºC during the day and this heat gets re-radiated
into the surrounding at night.
- Rooftop greenery reduces roof surface temperature by a maximum of 31ºC.
- Vertical greenery reduces wall surface temperature by a maximum of 12ºC.
- Temperature reduction efficiency varies with system typology, profile thickness, type of substrate,
- irrigation frequency, substrate water retention capability and plant shading coefficient.
The incoming solar radiation and heat gain through the roof can be reduced dramatically as well. – This translates to a marked reduction of re-radiated heat to the surrounding and into the building throughout the day. – The shading effects of plants is so good that they don’t just reduce heat from entering buildings but actually resulting in heat loss from the building.
“In Tokyo, the removal of greenery contributed to 0.6 ºC of the 2 ºC increase in temperature over the last 100 years.” (Hitosh, 2000 )
“Greenery can alleviate urban heat islands directly by shading heat-absorbing surfaces, and indirectly through evapo-transpirational cooling.” (McPherson, 1994)
“Greenery can reduce the amount of re-radiated heat. Only 20% of the sun’s energy that falls on a tree leaf is reflected” (Peck et al., 1999).
“A single tree can evapotranspirate 40 gallons of water in a day, offsetting the heat equivalent to that produced by one hundred 100-watt lamps operating eight hours per day” (Rosenfeld et al., 2000).
“Skyrise greenery mitigates the heat island effect through the vertical mixing of air. The warmer air above hard surfaces rises and is replaced by the cooler air above the green roof, thereby reducing the overall temperature” (Johnston, 1996).
“The composition of the roof and the type of vegetation may affect the temperature reduction capacity of the green roof. Thick, dark green greenery can reduce surface temperature better than sparse, red greenery” (Niachou et al., 2001).
2.) Improving the air quality by absorption of pollution and dust
“In Frankfurt, Germany, streets without trees had an air pollution count of 10,000-20,000 dirt particles per litre of air whereas a street with trees in the same neighborhood had only 3,000 dirt particles per liter of air” (Minke, 1982).
“Heated urban areas create vertical thermal air movements, which stir up dust particles found on the ground. Skyrise greenery can improve air quality indirectly through the reduction of surface temperature and thereby reducing thermal air movements” (Peck et al., 1999).
“Increased air temperature over roof surfaces contributes to the chemical reaction that creates low atmospheric ozone, which is the primary component of smog” (Schloz-Barth, 2001).
“Therefore controlling temperature through skyrise greenery can decrease ozone formation thereby improving air quality. However, consideration has to be given to the species of
vegetation planted as certain types of trees emit volatile organic hydrocarbons (VOCs) that combine with oxides of nitrogen to form smog” (Rosenfeld et al., 1997).
3.) Reducing the green house effect by CO2 absorption
4)Stimulating biodiversity through creation of additional natural habitats for birds and insects within the city
5)Rainwater retention: reducing and slowing the peak discharge to the drainagesystem and fewer ensuing floods
“In Berlin, Germany, the average green roofs absorb 75% of rainfall. Immediate discharge is reduced to 25% “(Kohler, 1989), “delaying surface runoff and reducing risk of flashfloods” (Liesecke, 1989).
”In Rio De Janeiro, green roof allows a significant reduction of the peak load during stormwater events. An annual retention rate of 65% is expected” (Kohler et al., 2001)
“Several peculiarities of the tropics may affect the water retention potential of green roofs. Firstly, frequent stormwater events may result in the potential erosion of newly implemented green roofs and the quicker saturation of the substrate. Secondly, high tropical temperatures may cause higher evaporation rate and gain in biomass, which presumably increases the water retention rate” (Kohler et al., 2001).
Total peak runoff rates are lowered through adoption of green roofs, limiting the risk and occurrence of flash floods.
6) Cultivation of vegetables and food
7) Savings in drainage infrastructure
The ability of green roofs to retain rainwater and lower peak runoff can aid in reducing the extent of storm water drainage infrastructure” (Schloz-Barth, 2001).
- The lower runoff generated through adoption of green roofs allows smaller storm sewers, which, in turn saves construction and maintenance costs of our drainage systems.