[Research] The Benefits of Green Roofs

Retention of rainwater to decrease peak flow and runoff

Green roofs are the most effective ways for stormwater management in urban neighbourhoods as the systems of vegetation and substrates can hold a significant volume of water. As a result, the risks of flash flooding in urban areas are decreasing. Vegetation/plant enhances evapotranspiration, and rising medium absorbs significant amounts of rainwater, resulting in decreased peak flow and runoff. Studies found that water retention (percentage) ranged from 55% to 88% by green roofs.

Source: Earthbeings

Green roof vegetation plays a crucial role in water conservation because each plant has its water conservation and transpiration ability. Every species of plants have different capacity for retaining water. Grasses, however, were the best for retaining the more water. The drainage system and a green roof gradient also impact the protection of green roofs from rainfall.

Improvement of water quality for the water utilization

Green roofs are the best methods for reducing stormwater runoff as well as enhancing the quality of water. Substrate removed the contaminants and heavy metals from rainwater and increased the quality of the water. Researches proved that the amount of ammoniacal nitrogen in green roof runoff is less than that of rainwater. They also indicated that the level of heavy metals from hard surfaces in urban runoff was substantially higher than the runoff from green roof layers.

The following factors are very critical for improving the quality of the runoff water from the green roofs:

• Plant Type

• Substrate type used on the green roof

• Rain intensity

• Regional (contains or does not contain emission sources)

• Green Roof Type (Intensive or extensive)

• Green-roof's age

• Drainage layer type

• Type of fertilizers used

• Organic content added to the substrate

Thermal advantages for improving the environment and reducing energy costs

The two essential functions of green roofing in urban areas are surface temperature control and thermal comfort. Green roofs provide thermal resistance to the building, which makes the building cool in summer and also lowers the energy costs. Green roof vegetation and substratum absorb less solar radiation than most other roof types and thus also saves money for cooling. Findings show that green performance can be seen significantly in the hottest and driest conditions

Source: Blog dos Engenheiros

A study showed that green roofs would lower the surface temperature by 30 °C to 60 °C. Research from China investigated the sedum green roofs for energy efficiency demonstrates that the annual reduction in cooling energy was 3.83%. Another analysis found that the green roofs saved about 20.9 percent in the daytime and 15.3 percent in the night. It would help increase the expense of the buildings' energy use in urban areas.

Air purification to natural comfort in urban areas

The green roof collects the toxic particles of fine dust from the air that could lead to human health in densely developed urban areas. In urban areas, air generally stored the particles of fine dust which damage and discomfort the urban environment. Green roofs manage to pacify the air pollution in two ways. First, the plants absorb by stomata the tiny contaminants in the soil. Second, the green roofs reduce the surface temperature that helps to meet energy requirements from fossils burning. Research has shown that a 1000 m2 green roof can capture dust of around 160–220 kg per year leads to an improvement of the area's environment.

Source: Ondugreen

It is attributed to the different qualities of the leaves and canopy structure of the plants. Deciduous shrub has the highest capacity to absorb more particles of dust while the herb has the least ability to absorb the particles of dust. Tree  are dominated to contain substantial amounts of particles of air dust

Noise reduction

Another advantage of the green roof is the noise level lowering; it is shown that vegetated roofs decreased noise level by 10 and 20 dB. A field experiment on green roofs tested green roof efficiency in reducing noise in urban areas. Results indicated that the vegetation has a high absorption coefficient which helps to reduce noise.

Source: Ondugreen

Ecological advantages

Various researchers have shown that green roofs are very effective in reducing habitat loss in urban areas. Green roofs also encourage exercise in urban areas. This encourages biodiversity by letting them enter green areas. This helps to turn impermeable surface areas into natural green areas and can also bring additional environmental benefits to urban areas.

Social benefits

Through incorporating the green space in urban areas, green roofs offer relief from concrete surfaces. Various research showed that the green roofs had the pleasant effect of decreasing air and noise emissions to urban inhabitants. Green open spaces grabbed the eyes sight and tried to bind people for roof gardening together. Green roofs also improve values for the properties. Furthermore, green roofs can provide potentials for urban farming; research has shown that all plants except pepper have produced adequate yield and are very useful for green roofs to produce food. Additionally, the results also indicated that more food production comes from proper selection of the vegetable type for food production and proper management in an extensive green roof.

Source: The London Rooftop Gym

Economic benefits

A few other studies have addressed that green roofs have several cost advantages, and they are typically economically feasible with the right design. The cost benefits of green roofs, however, are based on various factors such as the selection of the green roof system and the types of plant. The waterproofing membrane of a standard green roof is nearly 10–20 years old, and the green roof could last for over 50 years. Therefore, utilizing green roofs will bring high values and benefits to residents, neighbourhoods, and communities.

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Reference

Bianchini, F., & Hewage, K. (2012). How “green” are the green roofs? Lifecycle analysis of green roof materials. Building and environment, 48, 57-65.

Berndtsson, J.C., Emilsson, T., & Bengtsson, L. (2006). The influence of extensive vegetated roofs on runoff water quality. Science of the Total Environment, 355(1-3), 48-63.

Connelly, M., & Hodgson, M. (2013). Experimental investigation of the sound transmission of vegetated roofs. Applied Acoustics, 74(10), 1136-1143.

MacIvor, J. S., & Lundholm, J. (2011). Insect species composition and diversity on intensive green roofs and adjacent level-ground habitats. Urban ecosystems, 14(2), 225-241.

Whittinghill, L. J., Rowe, D. B., & Cregg, B. M. (2013). Evaluation of vegetable production on extensive green roofs. Agroecology and Sustainable Food Systems, 37(4), 465-484.