Urban Structural Density 2019

Methodology

Ascertainment of the Number of Storeys in Buildings

The number of storeys of a building was adopted from the Official Property Cadastre Information System (ALKIS). If a building features special or varied properties, the relevant data is subdivided and documented under ‘building components’. If a building has a ‘vertical structure’, i.e. a varied number of storeys, these are modelled as ‘building components’. This allows for a very fine differentiation of a structured building.

To derive the storey structure at ‘building component’ level, building parts with the following specifications were used:

• Low-rise part of building
• Part of building with a greater number of storeys (not high-rise)
• High-rise part of a building
• Basement
• Arcade
• Storeys that protrude/ are set back
• Other

All buildings without data concerning their number of storeys (number of above-ground floors = 0 and number of underground floors = 0) were automatically assigned a value of one above-ground floor. Components without a floor specification were not considered (except for the building type ‘basement’). Figure 1 presents an example of a building differentiation by components.

Fig. 1: Differentiation into the ALKIS object types ‘building’ and ‘building component'; left: block with buildings and right: block with buildings and building components.

Ascertaining the Site Occupancy Index

The site occupancy index (SOI) states the built-up proportion of a lot. The SOI is a decimal number with one or two fractional digits.

Thus, the formula to calculate the SOI used to prepare the present map is derived as follows: the sum of all built-up areas on a lot – here, the block or block segment area – is divided by the total area.

Since the building areas do not correspond to the block area boundaries, only the proportions of those building areas that actually lie within the block area boundaries were summed. To achieve this, the building boundaries were intersected with the block areas of Block Map 1 : 5,000 (ISU5). Building parts located outside of block areas, e.g. on traffic areas (road surfaces), were not considered.

Ascertaining the Floor Space Index

The floor space index (FSI) indicates the number of square metres of floor area per square metre of lot area, here at block or block segment area.

For ascertaining the FSI, the following applies:

The sum of all floor spaces of the main buildings and building components (cf. Fig. 1) located on a block or block segment area is divided by the block size. The floor area of a building is thus calculated by summing the areas of all full storeys. (Generally, this means: number of full storeys multiplied by the floor area of the building).

Consideration of Structural Facilities as per Article 19, Para. 4, BauNVO in ascertaining the Site Occupancy Index (SOI)

BauNVO defines two different parameters to calculate the site occupancy index. They differ in whether ancillary structures are included in the calculation.

According to Article 19, Para. 4, BauNVO, garages and carports, including their driveways and ancillary and structural facilities, are part of the floor area (cf. Tab. 1).

As a first step in the calculation, the “main facilities” as per Article 19, Para. 2, BauNVO, were ascertained. As a second step, the floor areas of garages, carports, underground car parks and ancillary structures listed in the ALKIS were added. The buildings of the types shown in Table 1 were categorised as ancillary structures if they had less than two storeys. As per Article 14, BauNVO, ancillary structures are not considered in the determination of floor space.

In cases where above-ground and underground structures overlap, the above-ground structures were cut out of the underground structures (e.g. in the case of an underground car park in a building).

To determine the site occupancy indices (SOI) presented in the map, only the main facilities as per Article 19, Para. 2, BauNVO were ascertained, disregarding ancillary structures. The map therefore does not display values including ancillary structures, i.e. garages, sheds etc. (Article 19, Para. 4, BauNVO), but these numbers were determined and can be accessed through the factual data display.

Tab. 1: Building functions and component types categorised as ancillary structures

Depending on whether Para. 2 or Para. 4 of Article 19 of BauNVO is referred to, slightly different urban structural density numbers emerge per block. Figure 2 shows the distribution amongst the selected SOI density classes for both calculation methods.

Fig. 2: The distribution of the site occupancy index (SOI) referring to Article 19, Para. 2, BauNVO or Article 19 Para. 4, BauNVO (excl. streets and bodies of water, area-weighted calculation), ALKIS building stock, March 2019.

Hereinafter, SOI always refers to the SOI based on Article 19 Para. 2 of BauNVO.

Overall, however, it turns out that this difference in considering ancillary structures only slightly affects the final presentation of the SOI.