Component: Green roofs
Description
Green roofs comprise a multi-layered system that covers the roof of a building or podium structure with vegetation cover/landscaping. The roof is likely to consist of an impermeable layer, a susbstrate or growing medium and a drainage layer (although not all green roofs require a drainage layer).
Green roofs are designed to intercept and retain precipitation, reducing the volume of runoff and attenuating peak flows.
Advantages and disadvantages
Advantages
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Mimic predevelopment state of hydraulics and hydrology
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Good removal capability of atmospherically deposited urban pollutants
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Can be applied in high density developments
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Can be retrofitted (reliant on site specifics)
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Ecological, aesthetic and amenity benefits
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No additional land take
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Improve air quality
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Help manage urban heat island impacts
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Insulates buildings against temperature extremes
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Reduces the expansion and contraction of roof membranes
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Sound absorption
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Disadvantages
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Cost (compared to conventional roof)
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Not appropriate for steep roofs
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Opportunities for retrofitting may be limited by roof structure (strength, pitch etc)
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Maintenance of roof vegetation
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Any subsequent damage to waterproof membrane likely to be more critical since water is encouraged to remain on the roof
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Where component can be used?
Residential: Yes
Commercial/industrial: Yes
High density: Yes
Retrofit: Yes
Contaminated sites: Yes
Sites above vulnerable groundwater: Yes
Performance
Peak flow reduction: Medium
Volume reduction: Medium
Water quality treatment: Good
Amenity potential: Good
Ecology potential: Good
Maintainence
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Irrigation is needed during establishment of vegetation for some roofs
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Inspection for bare patches and replacement of plants will be required on a regular basis
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Litter removal may be required (depending on setting and use)
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