With the amendment of the Building Code in 2013, a legal basis for the principle of “internal development before external development” was created for the first time. Paragraph 1a, paragraph 2 of the BauGB states:
Land is to be used sparingly and carefully; in order to reduce the additional use of land for structural uses, the possibilities for the development of the municipality are to be used, in particular by making land available for re-use, redensification and other measures for internal development, and soil sealing is to be limited to the necessary extent. Areas used for agriculture, forestry or residential purposes should only be converted to the extent necessary. The principles set out in sentences 1 and 2 shall be taken into account in the assessment pursuant to § 1 paragraph 7. The necessity of the conversion of areas used for agriculture or as forests shall be justified; in doing so, investigations into the possibilities of internal development shall be taken as a basis, which in particular may include brownfields, vacant buildings, gaps between buildings and other possibilities for subsequent compaction.
In the course of drawing up a development plan for the external area, municipalities must therefore weigh up the potential for internal development. In order to be able to legally identify a development plan, it is therefore necessary to record the inner-local area potential and obtain an overview of which of these areas can be activated for the real estate market – so to speak to prepare a potential area expertise.