When you get ready to build a facility or building in Germany....you come up against two German terms.
The first is Baugesetzbuch. This is the German federal book on building codes, which chiefly relate to property usage, property rights, safety related factors in construction, and general procedures of design. This book of codes....is approved out of Berlin and pushed across all sixteen German states.
The second is Bauordnung, which loosely translates to state building codes. This will lay out safety codes in a more defined fashion, construction practices acceptable in that state, and general rules on stability/safety (perceived by the experts in that state).
Sounding like a problem in getting projects approved state by state? Well, you could hire one national company to design a office building of a certain large size, and somewhere in the process find that they will end up partnering up with a local/regional design company who has the insight over the Bauordnung rules (that state's book).
Why no simplified national code and just dissolve the Bauordnung?
Well, this is a nation that was three-hundred separate entities until the early 1800s. As much as one might say it's one single country today.....it's really a federated republic of sixteen German states, and each has particular rules and understandings. They also have a compacted corruption factor where a certain party will control not only the construction codes but also controlling the construction permits. Whether you like it or not.....you could easily be pushed into several 'extras' that weren't part of your original plan.
An example of this....if you build a large significant building and depending on what state you are located in....there's typically a requirement for some type of landscaping 'art-works' to be part of the final design of the building. It's interpreted on what fits or what is accepted. You could put up a bold statue or piece of art.....layer the landscape with flowers and water-ponds.....or build the art-works into the look of the building itself. State-by-state.....it'd depend on what's in the Bauordnung and how the construction permit is written.
Bottom line....as much as people think that Germany operates under one single umbrella.....it's really a sixteen-umbrella theme, and depends much on where you are located.