Green roofs offer many advantages for building developers, owners and their users. They benefit the wider environment through their positive impact on sustainability, biodiversity and the attenuation of storm water. They create visual enhancement of the landscape and fully exploit the spatial opportunities for visual and recreational benefit with the possibility of planning gain.
Improved Air Quality
Green roof planting will improve air quality by absorbing atmospheric carbon dioxide and releasing oxygen. Airborne particulate pollutants are washed into green roof substrates via rainfall where they are filtered out. Plants and their growing substrate release water vapour so humidifying the air.
Roof Membrane Protection
Vegetation on a roof deck protects the roof surface from the extremes of weather, temperature and ultra-violet radiation, prolonging its life.
Rooftop habitats can provide a ‘green link’ connecting natural pockets of habitat with each other. They can also provide isolated habitats, which aren’t disturbed by other green areas at ground level. In Germany it has been shown that green roofs can harbour 10 – 40 different insect species and have been found to support nesting birds.
Urban greening has, for a long time, been seen as a way to make towns and cities look more pleasing to the eye, and be of great value to the well-being of building users.
Improved Temperature Regulation
In the process of evapotranspiration, plants use heat energy from their surroundings when evaporating water. Through the daily cycles of condensation and evaporation, plants are able to cool and humidify the surrounding air improving the microclimate.
Reduced Stormwater Run-Off
Water is stored by the green roof substrate and then taken up by the plants from where it is returned through transpiration and evaporation into the atmosphere. In summer, green roofs can retain 70 – 80% of the precipitation that falls on them; in winter they can retain 25 – 40%.
Green roofs also delay the time at which run-off occurs, resulting in decreased stress on drains and sewers at peak flow periods.
Reduced Energy Costs
The layers of a green roof system are able to improve the thermal performance of the roof, thereby reducing solar heat ingress into the building below. Rooms under a green roof can be at least 3° – 4°C cooler than the air outside when temperatures range between 25° – 30° C, therefore reducing the costs to condition the air temperature within the building. In winter the green roof can also help reduce heat loss through the roof.