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Evaluating Rooftop and Vertical Gardens

I recently came across a interesting piece of research with some great
supportive findings for the money Green Roofs and Walls can save. By performing
well financially, they also have the added benefit of helping the planet by lowering
fuel used to make energy and saving on waste water costs and impact. The
summary of the research findings in "Evaluating Rooftop and Vertical Gardens
as an Adaptation Strategy for Urban Areas" conducted by Environment Canada and the Institute for Research in Construction National Research Council is outlined below.
The researchers measured the differences in temperature profile, heat flow, solar
reflectance, rooftop microclimate, soil moisture content and storm water runoff and
performance (energy) between a Green Roof and a control roof (modified
bituminous).
If you would like the full report, drop me an email info@verticalplantscapes.co.za and I will send it to you.

Thermal Performance

􀁺 In spring and summer, the Green Roof significantly outperformed the reference roof - the vegetation and the growing medium enhanced the thermal performance of the Green Roof by providing shading, insulation and evaporative cooling
􀁺 The Green Roof also reduced the heat flow through the roof significantly
􀁺 During spring and summer, the average daily energy demand for space conditioning was reduced by over 75% (note that this reduction was due to the roof ONLY, other parts of the building envelope were not considered in this study)

(N.B Winter and Autumn in Canada being significantly colder than South Africa meant that thermal performance of the Green Roof was only slightly better than the reference roof as snow/ice froze the growing medium in sub zero temperatures)

Storm water Retention

􀁺 The Green Roof delayed runoff and reduced runoff rate and volume
􀁺 When the growing medium became saturated at least 2mm was absorbed before runoff occurred, and when the growing medium was dry, it was able to retain 8mm of water
􀁺 The Green Roof effectively delayed peak flow and reduced the rate and volume of runoff
􀁺 The Green Roof was an extensive system and it is expected that green roof systems with a deeper soil and more vegetation would have even higher storm water reduction potential
􀁺 Although not measured in this study, the green roof is likely to filter out pollutants that would be typically found in runoff from rooftops. As the surface is cooler, the runoff will be also be cooler, thus having less of an ecological impact in other bodies of water

Durability

􀁺 High temperature fluctuations accelerate the aging process in asphalt-based roofing membrane and reduces its durability
􀁺 The membrane on the Green Roof experienced a lower average in-service temperature and lower daily temperature fluctuations.
􀁺 It can be expected that rooftop gardens can help to preserve the membrane and prolong its service life by reducing heat aging and thermal stress
􀁺 Typically, a roof has a lifetime of 15-20 years, a green roof is expected to last 25-40 years.

Green Wall

􀁺 The Green Wall (vertical garden) was effective at reducing surface temperature and acted as a window shade
􀁺 The temperature behind the vertical garden was similar to the temperature of the vegetation canopy
􀁺 The effectiveness of using vertical gardens to shade building walls and windows on a three-story building was also tested which reduced the energy consumption by 23% for cooling and by 20% for air circulation

Evaluation of Adaptation to Warmer Temperatures

􀁺 Green roofs and vertical gardens were proposed as an adaptation to warmer summers and more frequent heat waves that could occur as a result of climate change which would be exacerbated in cities due to the urban heat island (UHI) effect
􀁺 Green roofs and vertical gardens are useful components to combat this by reducing indoor temperatures and to reduce the ambient temperature by a reduction in the UHI effect
􀁺 Green roofs and vertical gardens have been shown to achieve substantial reductions in the demand for air conditioning.
􀁺 While green roof infrastructure is most effective on one-story buildings r houses, vertical gardens are also effective on multistory buildings. Other Benefits of Green Roof and Vertical Garden Infrastructure Beyond the climatic impacts explored in this research, green roofs and vertical gardens are expected to bestow other benefits in urban areas. These include:
􀁺 improved air quality, due to the reduction in the rate of smog formation and the ability of vegetation to filter or absorb certain pollutants out of the atmosphere
􀁺 improved water quality due to the ability of vegetation to absorb some pollutants from water
􀁺 reduced environmental impact of storm water runoff due to the lower temperature of water from a green roof versus that from a regular roof increased biodiversity in urban areas
􀁺 increased green amenity space
􀁺 increased mental well-being
􀁺 increased property values
􀁺 increased job opportunities with the growth of a new industry in the economy

 

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