Green roofs are layers of vegetation planted over a waterproofing cover installed on flat or sloped roofs, serving to absorb rainwater, provide insulation, and create habitats for wildlife. There are several types of green roofs, the two main groups are extensive and intensive green roofs.   

Extensive green roofs are designed for minimal maintenance, covered with a lightweight layer of soil and drought-resistant plants such as sedums or meadow. They are typically not accessible for recreational use and are used for covering large areas or buildings unable to support heavier loads. Extensive green roofs are often possible to retrofit buildings. Extensive green roofs can, in principle, be installed at all roof angles, but costs may increase for steeper roof angles.  

Intensive green roofs are thicker, can support a wider variety of plants, including shrubs and trees, and require more maintenance. They are often designed to be accessible and also serve as social spaces and can include features like walkways, benches and areas for urban farming.   

Blue-green roofs extend the concept by incorporating water storage and management systems beneath the vegetative layer to handle excess rainwater more efficiently, combining the benefits of green roofs with extended stormwater management capabilities.  

Green and blue-green roofs as a stormwater measure are often applied in urban ecosystems. Their specific design and plant selection can vary to adapt to local climates, building regulations, and ecological goals. Beyond their direct impact on the buildings they cover, such roofs can positively influence surrounding ecosystems by reducing runoff into local waterways and regulating local temperature.  

Why

Green and blue-green roofs address environmental challenges such as urban heat island effect (climate change adaptation and mitigation), stormwater runoff (disaster risk and preparedness), and can also provide food for birds, bees and other pollinators in urban areas (biodiversity enhancement). They can also contribute to regulating energy consumption by regulating the temperature of the buildings and providing aesthetically pleasing green spaces for urban residents (human health and wellbeing).   

How

• Effects include reduced stormwater runoff, and mitigation of urban heat island effects and potentially increased urban biodiversity.
• Positive side-effects may involve improved air quality and increased property values.
• Blue-green roofs add significant stormwater management capacity, potentially reducing the need for traditional, ground-level stormwater infrastructure.
• Negative side-effects can include the use of invasive species that can spread to the ground if such are used.  

ATTENTION

How much do we know?

There is extensive research and numerous case studies demonstrating the effectiveness of green and blue-green roofs in urban environments, including in Nordic cities. Investigations on how to apply blue-green roofs to Nordic conditions are ongoing. This body of evidence highlights their versatility and adaptability to different climates and urban forms, from dense city centres to suburban developments. 

Costs

The implementation costs of green and blue-green roofs can vary widely, influenced by factors such as roof size, system complexity, and local labour and material costs. Operational costs include maintenance and, for blue-green roofs, management of the water storage system. Despite higher initial costs compared to traditional roofing, the long-term benefits in ecosystem services, energy savings, and stormwater management can justify the investment.