Good evening Tox,
A new building permit means, subsequently, that you also have to meet today's requirements!
Not necessarily. It depends on what was approved - according to the Energy Saving Ordinance 2007 or rather '09. The Energy Saving Ordinance 2007 was in effect, in my opinion, until autumn '09; the costs from 2007 to 2009 are relatively manageable and basically relate to insulation and energy consumption. Since so far "only" the bare shell has been standing, the costs for insulation and heating technology will occur anyway.
However, I agree with you that it is strange if a shell has been standing for years. Therefore, I would only buy if an expert gives me the green light and information about the expected costs.
Rhenish greetings