Green roofs – more than just a trend?

Green roofs have experienced a revival in Germany since the 1960s and have spread widely across Europe and the United States. The increasing popularity of green roofs can no longer be explained by their benefit for reducing air pollution in densely populated cities alone. Green roofs contribute to the environment and the quality of life in many different ways and yet there are many more advantages that are only evident at second sight. So let’s take a closer look.

1. Green roof
2. Advantages of green roofs
3. Financial incentives and benefits
4. Market development

What is a green roof?

A green roof is basically a planted rooftop. It is supposed to compensate for the vegetated footprint that was destroyed due to the construction of the building. Green roofs are differentiated into intensive and extensive green roofs. They differ in the underlying structure (depth of growing medium) and the types of plants used. The structure is very similar for both, adding several layers on top of the supporting structure (i.e. the rooftop):

On intensive green roofs, a wide variety of plant species including trees, shrubs and perennials that require “intensive” maintenance. They are often park-like structures that are accessible to the public and serve recreational purposes. Deep substrate layers are necessary and hence intensive green roofs are normally only installed on flat roofs.

In contrast, extensive roofs have smaller plants and require less maintenance. They have shallow roots and thus grow well on shallow substrate layers. Plants used include herbs, grasses, mosses and drought tolerant succulents. Extensive roofs are generally not accessible to the public but apart from that, they have the same benefits.

Can any roof be turned into a green roof?

Many but not all roof constructions are suitable to support a green roof. Concrete provides the most stable structure and is used most frequently but wood, metal, plastic, gypsum and composite constructions are also suitable. Of course, flat roofs lend themselves easily to be turned into green roofs while other surfaces present a greater challenge in terms of architecture and weight distribution.

Advantages of green roofs

Both intensive and extensive green roofs create an additional wildlife habitat by providing space for insects and birds, for example. Finally, there are interesting architectural and aesthetic aspects to consider as the basic idea of green roofs can also be applied to turn walls in and outside buildings into amazing pieces of art.

      • Improvement of the air quality

        by trapping air particles and gas pollutants that contribute to air pollution. Many of the pollutants are then washed away by rainwater while others are absorbed by plant tissue. Research has shown that one square metre of a green roof could remove 200g of dust particles every year.

      • Improvement of the drainage system

        Rainwater is stored and delayed by the plants. Through the temporary storage and delayed delivery, the local sewage systems are relieved during heavy or long-lasting rainfall

      • Reduced surface temperature of the roof

        The heating of the roof surface by solar irradiation is prevented. The reduced surface temperature of the roof prevents the heating of the rooms below

      • Function as sound insulation

        The roof greening reduces noise pollution.

    Financial incentives and benefits

    Investing in a green roof is well worth it – also in financial terms. Having a green roof can increase the lifespan of the roof and lower utility bills at the same time. Several communities in Germany encourage green roofs by providing grants, loans or other support. However, there are regional differences and there is a variety of different programmes:

      • Subsidies are typically 10-20 € per square metre or 25-100% of production cost
        In Munich, for example, green roofs are currently supported with 15 € per square meter (capped at 50% of total production cost) and a reduction of drainage fees of up to 70%.
      • Some communities may offer a reduction of drainage fees of up to 100%, which can be quite attractive as these are recurrent payments.
For more information, you can contact the relevant local administrative bodies (e.g. building or environmental departments).

A further financial advantage is the reduction of costs for heating and air conditioning as an attractive side-effect caused by green roofs. And finally, when you invest in a green roof you are not required to set up and maintain separate compensation areas.

How is the green roof market developing?

The European Federation of Green Roof Associations has collected data about green roofs within Europe. According to their 2015 report, there was a green roof stock of 86 million square metres in Germany in 2014 and about another 8 million square metres were added every year. Germany has the greatest share of green roofs within Europe with yearly sales figures amounting to around 250 million Euros.

green roof, Europe

Conclusion

Green roofs combine many benefits and play an important role in urban architecture. They help to improve quality of life in cities by reducing air pollution and creating green resorts both for residents and wildlife. A variety of plants can be used to create attractive, individual solutions depending on individual preferences. All in all, green roofs are well worth considering when planning your next building.

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