Every day, the amount of land used for residential, commercial and transport purposes in Germany increases by 51 hectares. The German government wants to change this. It wants to reduce the daily increase to less than 30 hectares by 2030. (Source: https://www.baden-tv-sued.com/mediathek/video/flaechenverbrauch-in-deutschland-waechst-taeglich-um-etwa-51-hektar/) The economical use of land is therefore one of the major challenges in building and planning practice. The German Building Code (Section 1a BauGB) explicitly obliges municipalities to use land sparingly and to observe the principle of „internal development before external development“ if they want to designate new areas for development. In municipal practice, it is therefore often a question of how far the municipalities must actually utilise this internal development before they are allowed to approach the outer area.

According to Section 1a (2) BauGB, local authorities should prioritise the possibilities of redensification and activation of inner-city potential before additional land can be made available in previously undeveloped outer areas. In practical terms, this means that the local authority must first systematically determine the potential for inner-city development, for example by means of vacancy registers, surveys of gaps between buildings or urban development analyses. Only when this potential is deemed to be exhausted for factual, legal or economic reasons may it seriously consider planning on outlying areas. This procedure is prescribed by legislation and case law.

As a generalised assertion that there are no opportunities for inner-city development is not sufficient in case law, a comprehensible and documented inventory is of great importance. Case law requires a differentiated individual examination of each development plan. In particular, it must be clearly explained which inner-city areas were specifically examined and why they are not suitable for the specific redensification. The municipality may therefore not simply ignore legally required alternatives for inner-city development or simply classify them as „cannot be activated“.

Due to these requirements, small and medium-sized municipalities in particular often find themselves in a complex area of conflict between legitimate development interests, limited resources for processing existing properties and the strict verification requirements of building planning law. The most frequent problems are caused by the inadequate, unsystematic documentation of inner-city development potential. Without a reliable land survey, there is neither a solid forecast of the actual demand for building land, nor can it be justified why there should be no alternative to planning in external areas. This would not only be a violation of the urban planning necessity pursuant to Section 1 (3) BauGB, but also of the balancing requirement pursuant to Section 1 (7) BauGB.  

A common misunderstanding also concerns the assumption that planning on greenfield sites is always legally permissible as soon as a municipality pursues certain economic development goals. However, this is not the case, as the provision of Section 1a BauGB requires that the consequences of increased land consumption are explicitly addressed. It must also be justified why inner potentials cannot be mobilised as a priority or subordinate in the specific case. For example, established case law requires planning authorities to openly present conflicting objectives, make coping strategies plausible and present reliable documentation during the planning process. If this does not succeed, local authorities run the risk of the development plan being declared invalid in legal review proceedings. This is then regularly associated with considerable follow-up costs, reputational damage and planning uncertainty for investors and for municipal development as a whole.

Local authorities should therefore attach great importance to the requirements of Section 1a BauGB and make measures for the documentation, evaluation and activation of inner-city development potential a matter of course. In the event of a dispute, structured evidence and a robust examination of supreme court rulings are the only way to secure and legally safeguard successful planning and development projects. With the necessary care, transparency and legal support, the room for manoeuvre of municipal planning can be preserved and a sustainable, legally secure settlement policy can be created