Green Roofs 2020


Green roofs have a positive impact on the environment and therefore help to counteract the impairment of the natural balance in conurbations. They reduce rainwater runoff, create evaporation surfaces and may even increase biodiversity (DBU 2011). Offering the possibility of creating additional green spaces for recreation and activity, green roofs contribute to improving the urban residential environment.

Roof greening measures, as an element of adding green roofs to both new and existing buildings, aim to relieve the burden on the sewage system, improve the air quality, cool the urban climate as well as strengthen the biodiversity. Furthermore, roof greenery reduces noise levels and adds greatly to the cityscape. These positive effects also help to boost the urban population’s health when it comes 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 highlights the role of green roofs and facades for the health of the urban population in their green paper “Green Spaces in the City” (BMUB 2015).
Green roofs may reduce the problems of an impervious city, such as urban heat islands. As an element of rainwater management, they may also relieve the burden on surface waters (SenSW 2017a). Planted roofs lead to a better retention of rainwater. The reduction in rainwater runoff alleviates the strain on the sewage system (SenStadt 2010).

Since the year 2000, domestic wastewater and rainwater charges have been billed separately. Rainwater charges are based on the impervious areas of a property. Areas with no or very little impact on rainwater discharge are either disregarded or taken into account partially in the calculation process. For green roofs, for example, only 50 % of the area is included in the calculation (SenJust 2016, BWB 2021).

Greenery on roofs and facades has been a part of Berlin’s story for a long time. At the beginning of the 19th century, Berlin already featured about 2,000 green roofs, in the form of wood-concrete roofs (Ahrendt 2007).

In West Berlin, a “courtyard greening programme” was initiated in 1983. The goal was primarily to mitigate green space deficits in the inner city. The programme offered funding for courtyard, facade and extensive roof greening measures. East Berlin also had a “courtyard greening programme” in the 1980s. Starting in 1990, the programme, which had been developed in 1983, was carried out in the entire inner-city area of Berlin. This was followed by guidance on how to preserve and maintain the facilities. The programme ran from 1983 to the end of 1995. During this period, 1,643 projects were approved, 740,000 m² of courtyard and facade areas, and 65,000 m² of roof areas were greened (Reichmann 2009).

As early as 1990, ecological requirements were defined in the guidelines on public funding for social housing, stipulating that resource conservation and environmental compatibility should be considered in building projects. Eligible for funding were, for example, vegetation concepts for facade and roof greening, as well as particular ecological open space concepts and their implementation.

Since 1992, ecological planning criteria have been in place for competitions. They state that “compensatory measures, such as roof gardens or roof and facade greening are particularly helpful in densely built-up inner-city areas […]” (SenStadt 2019). Green roofs and facades are also important components of general ecological concepts focussing on buildings; exceptional ecological building projects in Berlin may be found here (SenSW 2017b, SenSW 2017c).

The biotope area factor (BAF) is a special way of securing “green qualities” in the inner city to mitigate open space deficits and reduce environmental burdens. In Berlin, the BAF may be stipulated as a legal ordinance in a landscape plan. It describes the area share of a property that is vegetated or plays a role in the natural balance, therefore including green roofs (SenUVK 2021).

Since 2019, the “GründachPLUS” (Green Roof PLUS) funding programme, formerly known as “1.000 grüne Dächer” (1,000 Green Roofs), has been promoting the planting of greenery (> 100m²) on existing buildings, particularly in high-density urban quarters (SenUVK 2019). As there is currently no legal obligation to add green roofs to existing buildings, public funding is a very important measure here (Abgeordnetenhaus Berlin 2022).

The available data on existing green roofs may be used for various purposes. They may also be used as a basis for rainwater management concepts in urban areas and as a data basis for climate modelling. The data also serves as a basis for continuously monitoring the development of green roofs. Moreover, the available inventory of green roofs may also be used to develop future green roof strategies. For this purpose, it would also be important to determine the untapped green roof potential in the city.