Given the acute demand in many places for increasing the provision of building land and the opposite goal of reducing land take, reliable basic data is essential for sustainable land management. The main objective of the project was therefore to collect current data and information on building land reserves and infill development potential as well as on the status and methods of building land inventories and mobilisation in German cities and municipalities. The project was commissioned by the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR) and carried out in cooperation with the German Economic Institute (IW). The survey was supported by the German Convention of Cities and the German Association of Towns and Municipalities.
For some years now, the discussion on land use in the context of settlement development has been dominated by two main issues. On the one hand, the limitation of new land take and the protection of soil are central goals of sustainable development of the built environment at international and European level as well as in national programmes. Responsible use of global land resources is seen as an essential cross-cutting element in achieving the Sustainable Development Goals. At the European level, the current EU Soil Strategy for 2030 (European Commission 2021) once again explicitly emphasises the goal already set out in the Roadmap to a Resource-Efficient Europe to "reduce land take, so that by 2050 no more land is consumed on a net basis" (European Commission 2011). The German Sustainability Strategy as well as the coalition agreement of the parties of the current Federal Government (lines 1316-1318) concretise this concern with the goal of limiting daily new land take to less than 30 ha/day by 2030.
On the other hand, the Federal Government aims to build 400,000 new flats per year. It thus addresses the great need – especially in settlement areas under growth pressure – for an increased and accelerated provision of building land. If this does not succeed, prices and rents threaten to rise further and affordable housing will become so scarce that not all households will be able to provide themselves with sufficient living space. In order to ensure an adequate supply of housing, the Building Land Commission drew up proposals in July 2019, which also include the recommendation for improved databases on building land and greater transparency of building land potential and demand (cf. Building Land Commission 2019).
At the same time, a regular, nationally comparable survey of core content and data for land management and building land monitoring is still not being carried out in Germany. The most recent cross-sectional surveys available nationwide are building land surveys from 2003 and 2006 and a survey of infill development potential from 2012.
Accordingly, the main objective of this project was a nationwide survey of building land and infill development potential. The survey of cities and municipalities serves as an up-to-date knowledge base for an informed conception of a sustainable building land supply. The project team surveyed potential land and reserves for residential, commercial and other uses as a basis for both nationwide and regionalised projections differentiated by spatial types. On this basis, a comparison was made between potential land and housing needs, including an estimate of the potential housing that could be realised on the land. In order to be able to understand development trends, the project team also compared the current results with those of a survey from 2012 on the potential for infill development (cf. BBSR 2014).
In addition to quantifying building land and infill development potential, another focus of the survey was on assessing the situation and development trends in the preparation of land inventories and land management. This concerns both the content (brownfield sites, vacant plots, vacancies, etc.) as well as the practices and digital solutions used such as land management systems, data-bases, tools, etc.
The third major concern of the study was to collect data on the actual availability of building land and infill development potential as well as mobilisation activities. The project team determined the actual availability of potential building land and identified promising approaches to building land mobilisation. To this end, in addition to the results of the survey, it also analysed in-depth qualitative case study investigations.
The researchers also evaluated existing national, federal state-specific and municipal examples as well as instructive international activities and experience of building land inventories and the mobilisation of potential building land.
The contractor for the research project was the Leibniz Institute for Ecological Urban and Regional Development in Dresden in cooperation with the German Economic Institute in Cologne.
The overall research design of the Building Land Survey 2020 was based on three methodological approaches:
In the preparatory research, the project team reviewed existing experience, approaches, methods and tools for the preparation of building land inventories and mobilisation. It looked at initiatives at the different federal levels (national, federal states, regional planning, municipalities). This research was complemented by an investigation of some international approaches that could also be relevant for Germany as best practice examples. The analysis also aimed to concretise the scope of investigation for the actual building land survey, i.e. to determine, which types of land are to be included (definitions).
At the core of the project was the preparation, implementation and evaluation of the Building Land Survey 2020 as a standardised online survey. In terms of content, it was based on core content of the questionnaire of the Infill Development Study of 2012 (cf. BBSR 2014) as well as on the Residential Building Land and Commercial Building Land questionnaires of the Building Land Survey of 2006. The project team developed the content of the questionnaire in several pretest rounds and an online workshop with experts from research and practice. Representatives of the municipal umbrella organisations which supported the survey, were also involved in the development process. Finally, almost 3,000 cities and municipalities were contacted (gross sample), also in coordination with the municipal umbrella organisations. The sample included all 1,593 (31.12.18) cities and towns with 10,000 or more inhabitants, about 50% of the towns and municipalities with 5,000-9,999 inhabitants and about 10% of the small rural municipalities with less than 5,000 inhabitants. The link to the online questionnaire was sent out by email to the relevant administrative departments in July 2020. After various follow-up actions, the survey was completed at the end of 2020. A copy of the questionnaire can be accessed here (German only).
In addition to the survey, the project team subjected several systematically selected municipalities of different spatial types and development contexts to more intensive analysis. These case study investigations were conducted together with local practitioners. The central aim here was to expand and deepen the basic research and to identify innovative and pioneering approaches and experience of preparing land inventories and mobilising the potential of building land. In addition, they served to qualitatively underpin the results of the standardised survey.
The studies aimed to answer the following key research questions:
Nationwide representative questionnaire survey
The response to the Building Land Survey 2020 amounts to a total of 1,084 raw data sets. After completion of data cleansing, the final net sample comprises usable data records from 692 cities and municipalities and thus represents just under a quarter (23.1%) of the municipalities contacted for the building land survey. This is a total of 6.4% of the municipalities in the basic population of all German cities and municipalities (cf. Table 1).
|Municipality size classes|
by number of inhabitants (inh.)
Number of municipalities
Number of gross
related to contacted
|% response related|
|100.000 – 499.000 inh||67||67||27||40,3||40,3|
|20.000 – 99.999 inh||621||621||159||25,6||25,6|
|5.000 – 19.999 inh||2.251||1.549||345||22,3||15,3|
Table 1: Overview of the return of validated questionnaires in five municipality size categories (population as of 31.12.2019); Source: Calculations and illustration IOER, commissioned by BBSR
The following presentation of key results is limited to an overall perspective. Differentiations, for example, along regional types and municipality size classes, can be found in the corresponding publications (in German language).
Land development potential and reserves
The land-related scope of the survey comprises the three main land development capacity categories of infill development potential, further building land reserves with secured development and ready for construction, and additional long-term building land potential (as designated by development plans and land use plans).
Infill development potential
Based on the information provided by the respondents, IDP of at least 84,000 ha can be extrapolated nationwide. In terms of inhabitants, this corresponds to a total of around 10 m² per capita or, in terms of settlement area, to around 4% of the settlement area for housing, industry and commerce (HIC). Compared with the approximately 120,000 ha extrapolated as a lower limit in the IDP survey in 2012 (BBSR 2014), the current value represents a decline of around 36,000 ha.
Of the approximately 84,000 ha of IDP identified, just under 40% is accounted for by brownfield sites and more than 60% by vacant plots. The respondents' figures on IDP based on available data tend to be higher than estimated figures. Assuming that more valid information was provided on the basis of available data, an upper estimate for IDP of around 106,000 ha can be determined by means of correction estimates. This value was approximately 165,000 ha in 2012. It is interesting to note that this IDP, which has been reduced in absolute terms, is of a fundamentally comparable order of magnitude in relation to the average new land take, which has also been reduced compared to 2012.
Further developed building land reserves ready for construction
In addition to the IDP, the project team surveyed further building land reserves with secured development and ready for construction. The aggregated extrapolation of IDP and such further building land reserves results in around 99,000 ha of total building land potential as a validated lower limit. Here, the upper estimate is 132,000 ha. The cities and municipalities estimate around 55% of this total building land potential as being directly usable or able to be mobilised in the short term. Among the planned uses, housing is in first place on around 65% of the land, followed by commercial on just under 25% of the land. Areas for green space and recreation are planned on only about 3.5% of the areas, which is significantly less than their current share of over 10% of the overall settlement and transport area. The remainder is for other or unknown uses.
Depending on urban density assumptions with respect to dwelling units (DU) per hectare and for only the portion of the total building land potential of around 99,000 ha that can be used directly or mobilised in the short term, between just under 900,000 and just over 2 million dwelling units can theoretically be implemented on the portion of land earmarked for housing. This compares with an assumed housing demand of around 1.5 million units by 2025, based on calculations of the housing demand model of the German Economic Institute (IW). Moreover, depending on assumptions – with reference to upper estimate, consideration of longer-term potential, assuming higher densities for example – the housing construction potential can theoretically increase to more than 4 million dwelling units (not including land inflows that are not foreseeable today, but which experience has shown to be realised). However, this would require a considerable change in current planning realities and demand preferences. Table 2 shows a differentiated presentation of realisable housing units for the different categories of building land reserves and potential and according to different calculation methods.
Additional long-term building land potential
With regard to the third category of additional long-term building land potential, the information provided by the respondents adds up to about 34,000 ha of development plan potential (greenfield land without secured development) and about 100,000 ha of land use plan potential. Processes to establish building rights have been initiated for a total of almost 70 % of the development plan potential and almost 40 % of the land use plan potential. These long-term potential values are not included in the above estimate of possible housing potential, but can increase them. Table 2 shows the orders of magnitude. Figure 1 shows an overview of the different categories of surveyed (building) land reserves and potential in relation to the settlement area for housing, industry and commerce (HIC).
|Method (3) |
|Type of potential↓||Hectares|
|Million DU||Million DU|
min – max
min – max
|Infill development potential (IDP)||84.400||1,407||1,750 – 3,500||1,439 – 2,878|
|total building land potential|
(IDP + further building land ready for construction)
|98.900||1,648||2,065 – 4,130||1,647 – 3,294|
|…thereof directly or in the short term available||52.700||0,879||1,117 – 2,234||0,898 – 1,796|
|Additional long term development plan potential||34.200||0,570||0,648 – 1,296||0,487 – 0,973|
|Additional long term land use plan potential||99.900||1,666||1,992 – 3,984||1,480 – 2,960|
Table 2: Estimation of realisable dwelling units (DU) under different assumptions: Average density assumption (Method 1) as well as differentiated densities along BBSR district types (Method 2) or municipality size classes (Method 3); Source: Calculations and illustration IW, commissioned by BBSR
A direct comparison of the total building land potential with regional needs shows a weak negative correlation between needs and potential. However, the differences are only small. While around 45% of the cities and municipalities surveyed in districts with very low building land needs have high or very high potential, this figure is only just under 40% in districts with very high needs.
Insofar as the cities and municipalities provided information on additional land requirements over and above the existing total building land potential, it is particularly noticeable that the land requirements for single-family and two-family housing are consistently higher than the land requirements for multi-storey housing. Around 75% of the additional building land requirements for housing are needed for detached and semi-detached houses, only 25% for multi-storey housing.
Land inventory practices
At least with regard to the categories of brownfield land, vacant plots and vacancies which were also surveyed in 2012, there is clear progress in the dissemination of land inventory approaches. For example, for the most frequently surveyed category of vacant building plots, a total of around 50% of the cities and municipalities now report municipality-wide survey coverage, compared to only around 30% in 2012. When the categories ‘municipality-wide survey’ and ‘survey for selected areas’ are considered together, vacant plots, land use plan potential, building land reserves ready for construction and development plan potential (greenfield land) are at the top of the data collection activities, with over 50% of the cities and municipalities having such measures in place in each case. These categories are also at the top of the list when it comes to updating the data. Between about 40% (vacant plots) and about 30% (land use plan potential) of the data-collecting cities and municipalities report regular annual updates.
With regard to instruments for residential land development, the researchers asked about the relevance of legal instruments and more general strategies. Among the legal instruments, the respondents attribute the highest importance to ‘qualified’ development plans i.e. those in which at least the type and extent of building use, the area of the site that can be built on, and the local road infrastructure are specified. More than 50 % of the respondents see a major contribution here, and another 30 % see a relevant contribution. The second and third places are taken by the development plan for infill development in accordance with Section 13a of the Building Code (BauGB) and the simplified procedure for newly developed areas in accordance Section 13b of the Building Code. Here, around 18% and 20% of the cities and municipalities respectively see a major contribution of these instruments. Measures according to Section 13b of the Building Code are considered to be of major or relevant importance especially by the small towns and rural municipalities, while such measures are of lesser importance in the large cities.
When considering more general strategies of residential land development, the respondents attribute great importance in particular to classic supply planning. More than 70% of the cities and municipalities see a major or relevant contribution here. The development of municipally owned land by the municipality and of private land by private actors on the basis of an urban development contract or a project-related development plan, follow in importance. Around 45% of the cities and municipalities see a major or relevant contribution of the first approach and around 35% do so for the latter. The development of residential land in inter-municipal cooperation plays almost no role at all.
In addition to the question about instruments and strategies, the project team also asked about the applicability of various general land use policy orientations. Here, the respondents most frequently indicated a demand-oriented development of building land. This approach applies ‘fully’ in about 35% of the cities and municipalities and ‘rather’ in another 48%. A clear ‘quantitative limitation of new building land designation’ as well as an explicit commitment to the ‘priority of infill development’ are stated by around 23% and 20% of the cities and municipalities respectively (‘fully agree’). In another 25% or – with respect to the priority of infill development – in nearly half of the cities and municipalities, respondents stated these orientations ‘rather’ apply.
This shows an increase in the importance of infill development measures compared to the IDP study of 2012. In 2012 the similarly worded statement: ‘brownfield land and vacant plots are developed as a priority over newly designated areas’ was only agreed to ‘fully’ by over 10% and ‘rather’ by over 30%. On the other hand, the topic of double infill development – an approach combining infill building measures with urban green development – has lost importance in one respect compared to 2012: Only around 6% of the cities and municipalities ‘fully’ acknowledge the great potential of brownfield land and vacant plots for non-building development (renaturation, green/recreation areas, etc.) (2012: 10%), and about 20% ‘rather’ agree with the statement (2012: 30%).
Desktop research on current the status of building land inventories and mobilisation
The results of the desktop research conducted by the research team in the run-up to the survey show that the importance attached to the topic of preparing inventories of land development reserves and potential varies greatly between the federal states. While 11 of the 16 German federal states have database systems that explicitly address the issue of preparing building land inventories at the municipal level, it also became clear in the survey that the use of these services varies greatly. For example, 74% of the cities and municipalities from Rhineland-Palatinate participating in the survey use the tool RAUM+Monitor, while in other federal states similar available systems are used less or hardly at all. There are various reasons for this. The tools are only obligatory in some cases, for example to prove the necessity of developing new residential areas to regional planning authorities (Rhineland-Palatinate) or in the context of funding applications (Thuringia).
Furthermore, the case study investigations showed that the low use of the systems can also be due to the fact that in some federal states they are still being developed or are already outdated. This can lead to cities and municipalities hardly using them and rather resorting to their own more up-to-date systems. New initiatives would therefore be helpful to support municipalities in meeting the demands of land management with modern methods and systems. In terms of content, the methods of conducting (building) land inventories generally focus on surveying land development reserves and potential in inner urban areas and the recording of vacant plots and brownfield sites. All tools use similar, but not uniformly defined terms and categories. The case study investigations also revealed this as a difficulty.
Typical instruments for mobilising building land potential are publicly accessible registers of vacant plots, real estate and plot exchanges, targeted funding programmes for filling vacant plots or strategic municipal purchases of land for medium-term development and meeting building land needs. However, a frequently discussed prerequisite, and sometimes also a hurdle, is the willingness of landowners to cooperate. Accordingly, as reported in the survey the most common approach was targeted communication with landowners.
With regard to international experience, the project team examined activities and examples from Switzerland, Luxembourg, Austria, United Kingdom, the European Union and the United States of America. Despite all the differences in terms of economic and demographic development, planning culture and the planning autonomy of municipalities, commonalities could also be identified. For example, in all countries with regions undergoing structural change, the revitalisation of brownfield land is a priority. But the use of vacant plots and the avoidance of vacancies are also important topics. For example, the ‘call for sites’ approach in the United Kingdom is an interesting one. Here, not only landowners, but also the general public is explicitly addressed to put forward potential sites for which it is assumed that development is necessary or suitable. An international example of financial support for municipalities in the systematic activation of unused existing land is the ‘Brownfields Program’ of the US Environmental Protection Agency (EPA). An example of supra-regional initiatives as a basis for strategies and cooperation for land development above the municipal level is the Swiss ‘Raum+’ procedure, which operates there at the cantonal level.
Case study investigations
As a starting point of the case study investigations, the research team conducted explorative interviews with 21 cities and municipalities. They included municipalities with different settlement structures and demographic characteristics as well as those with particularly interesting approaches. On this basis, the next step was to conduct more intensive case study investigations in five selected municipalities.
By conducting inventories of land reserves and potential, municipal actors lay the foundations for informed decision-making processes and sustainable land management. The main objective is on the one hand to activate already used and developed land in the existing settlement area, and on the other to monitor changes, especially new land potential. There are very different approaches with regard to the specific design of the data collection methods, updating and maintenance of the databases. From the point of view of the municipalities, it is important that the corresponding tools are user-friendly and ideally have interfaces that allow automated data exchange between administrative units and authorities. However, the need to develop general overarching standards for the design, scope and procedures of land inventories was also discussed.
However, according to the results of survey and case studies, the most important obstacle to the systematic collection and maintenance of land use data is the limited capacity of personnel. For example, under conditions of population decline, when in doubt, municipalities will rather intensify targeted efforts to address landowners instead of conducting complex, detailed land surveys. The establishment of qualified personnel thus represents the core challenge for cities and municipalities in establishing successful land management. Figure 2 shows an overview of the key results of the Building Land Survey 2020.
Conclusion and outlook
Overall, the results of the Building Land Survey 2020 and the supplementary qualitative case study investigations provide a representative overview of the magnitudes of land reserves and land potential as well as of the status and methods of conducting building land inventories and land management in Germany's cities and municipalities. In principle, the extent of the response also allows evaluations below the national level, for example along municipality size classes, growth dynamics, settlement-structural district types or groups of federal states. Even if the respective smaller-scale results are associated with higher uncertainties due to the basically nationwide conception of the survey, it was nevertheless possible to generate differentiated insights. In particular, the basically identical approach enables a comparison between the recent findings and the situation at the time of the survey of infill development potential conducted in 2012 and thus to identify changes.
With at least 99,000 ha of total land reserves and potential, based on conservative assumptions between just under 900,000 and just over 2 million dwellings can theoretically be realised on the proportion of land earmarked for housing which can be mobilised in the short term. This directly available potential alone corresponds to about 60–133 % of a housing demand of about 1.5 million dwelling units assumed on the basis of the housing demand model of IW up to the year 2025. Furthermore, depending on the assumptions, the housing construction potential can take on considerably larger dimensions and theoretically rise to more than 4 million dwelling units (not including land inflows that are not foreseeable today, but which experience has shown to be realised).
It is against the background of this overall existing and not inconsiderable land potential, that the further fundamental orientation towards the priority of infill development is necessary. This applies in particular with regard to the goal of limiting the daily new land take in Germany to at least less than 30 ha by 2030. In many cities and municipalities, the priority of infill development is still a realistic option. This is a way of creating a lot of living space. However, the concept of a ‘double infill development’ must not be lost sight of. The Covid-19 pandemic in particular has once again emphasised the importance of open spaces and recreational areas close to residential areas.
Regardless of the respective local situation, comprehensive knowledge of the existing land potential is an essential basic condition for targeted land management. The results of the survey suggest that cities and municipalities with an appropriate data collection have a more complete view of their land reserves and potential. In order to remedy the existing capacity problems, especially in smaller cities and municipalities, it appears advisable to support higher-level initiatives and offers of (building) land inventory systems. This also includes publicising appropriate land management tools and informing actors about the benefits of using these tools uniformly in the various municipalities, such as saving them the effort of developing their own methodological tools. However, such tools must also be kept up to date in terms of content and technology. Indications from the case study investigations suggest that instead of using existing overarching applications, more up-to-date and more powerful proprietary solutions are sometimes preferred.
An important aspect of the further development of land inventory approaches is the expansion of interfaces to other databases and institutions, including the development of common standards. As long as no comparable nationwide data is available, the instrument of the building land survey will remain particularly important. It would in this case remain the only way to obtain a comprehensive orientation on existing land reserves and potential and the current status of (building) land inventory approaches and land management practices in German cities and municipalities.