Buildings were classified into six “building use” categories based on the use information from ALKIS and NOT-ALKIS. Table 2 and Figure 3 illustrate the size and percentages of building uses that include green roofs.
With percentages ranging between 22 and 30 % (Fig. 3), green roofs [m²] are relatively evenly distributed across the building uses “Residential” (incl. weekend cottages), “Non-residential buildings” (e.g. schools, town halls, retirement homes, administrative buildings), “Office buildings, commercial” and “Underground car parks without superstructures”. Compared to rooftop greenery, that of underground car parks tends to be more comprehensive and denser (Fig. 3). The ratio of intensive to extensive greenery on underground car parks is about 80 % to 20 %, on building surfaces it is the reverse.
In addition, Table 2 identifies potential for future green roofs. So far, only 3.4 % of buildings in the “Office buildings, commercial” category, which are expected to have flat roofs for the most part, have green roofs. The green roof potential is therefore high. By contrast, and, as expected, this potential has been tapped into much more at 77 % in the category of underground car parks without superstructures. This is the case, although the proportion of greenery varies across the roof surfaces of underground car parks (Tab. 2).
One might also expect a larger proportion of green roofs on garages and sheds. This is complicated by the issue, however, that green roofs frequently remain undetected on these often rather small rooftops due to large tree canopies and are therefore not recorded during the mapping process. As a result of the TrueOrthophotos recorded in summer (August), this occurred more frequently in the course of the 2020 mapping compared to the 2016 mapping. The actual proportion of green roofs is therefore assumed to be higher in this building use category.