Green Roofs 2016
Due to their positive ecological functions, green roofs contribute to reducing the impairment of the ecosystem in metropolitan areas. They reduce rainwater runoff, create evaporation surfaces and may increase biological diversity. Due to the possibility of creating additional greened areas where people can stay or engage in activities, they contribute to improving the urban residential environment.
Roof greening measures, as an element of greening both new buildings and the building stock, aim to achieve relief of the sewer system, improvements in air hygiene, cooling effects on the urban climate as well as strengthening species diversity. Greening buildings has further positive effects in that it reduces the noise level and enriches the cityscape. All these effects also contribute to promoting the health of the urban population with a view to climate adaptation (SenStadtUm 2016, SenStadtUm 2016a).
At the national level, this approach is supported by an initiative of the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), which in its current “Green Paper Urban Green” emphasises the role of greening roofs and facades for the health of the urban population (BMUB 2015).
Roof greening as an element of rainwater management can reduce problems of the sealed city such as urban heat islands and decrease the load of the surface waters (SenStadtWohn 2017a). Planted roofs lead to improved rain retention. The reduction in rainwater runoff relieves the sewer system (SenStadt 2010).
Since 2000, the charges for domestic wastewater and precipitation water are being billed separately in Berlin. In determining the sealed surfaces as a basis for the charges for draining the precipitation water, it is taken into account that surfaces that have little or no influence on the precipitation water runoff are not or only partially considered in the calculation of the fee for precipitation water disposal. For instance, for greened roof areas only 50 % of the respective area is considered in calculating the precipitation water fee (SenJust 2016, BWB n.d.).
Greening roof and facade surfaces has a long tradition in Berlin. At the beginning of the 19th century, there were already about 2,000 green roofs in Berlin, which were constructed as wood-cement roofs (Ahrendt 2007).
In West Berlin, a “courtyard greening programme” was initiated in 1983. The goal was primarily to reduce the green space deficits in the inner-city areas. The programme offered funding for measures for greening courtyards, greening facades and extensively greening roofs. East Berlin also had a courtyard greening programme in the 1980s. Beginning in 1990, the programme developed in 1983 was carried out in the entire inner-city area of Berlin, and advice on the preservation and maintenance of the facilities was provided. Over the course of the programme from 1983 to the end of 1995, 1,643 projects were approved, and 740,000 m² of courtyard and facade surfaces and 65,000 m² of roof areas were greened (Reichmann 2009).
Already in 1990, ecological requirements were defined in the guidelines on public funding for social housing, according to which resource conservation and environmental compatibility are to be taken into account. For example, vegetation concepts for greening facades and roofs as well as special ecological open space concepts and their implementation were eligible for funding.
Since 1992, ecological planning criteria are established for competitions in Berlin. They assert that “compensation measures in the form of roof gardens, roof and facade greenings make sense in particular in densely built-up inner-city areas […]” (SenStadt 2007). Greening roofs and facades is also an important component of building-related overall ecological concepts; outstanding projects in the area of green building in Berlin can be found here.
In the inner city, the “biotope area factor” (Biotopflächenfaktor, BFF) constitutes a particular form of ensuring “green qualities” to compensate deficits in free space and to reduce environmental loads. In Berlin, the BFF can be prescribed by ordinance in a landscape plan. It designates the area proportion of a plot that serves as a plant site or assumes functions for the ecosystem, and thus includes green roofs (SenUVK n.d.).
The data that are now available on the stock of green roofs can be used for different purposes; they can form the basis for concepts of rainwater management in the urban space and likewise for continuous monitoring of the further development.
Moreover, the available inventory of green roofs can also be used for a future greened roof strategy. A determination of the further potential for green roofs in the city would be an important supplement for this purpose.