The application of the simplified procedure has nothing to do with the clarity of the examination effort, but rather with the requirements mentioned in §62.
That’s also what I meant – so not related to the examination effort in the individual case, but to the type of construction project. The mentioned paragraph defines the suitable construction projects as follows:
"The building supervisory authority examines for 1. residential buildings of building classes 1 to 3, 2. other buildings of building classes 1 and 2, [...] a) compliance with the regulations on the permissibility of structures according to §§ 29 to 38 of the Building Code, b) adherence to the requirements according to this law and the regulations issued pursuant to this law, and c) adherence to other public-law regulations."
This outlines the suitable building types and also the regulations to be checked for compliance. Conversely, it follows that building types assigned to other classes (for which additional regulations would also have to be demonstrated to have been observed) do not meet the requirements and in any case require a more complex procedure.
As far as I can see, the present case concerns a measure in an area without a development plan (= indication against the positive extreme of exemption), but in a residential building with few residential units (= indication against the negative extreme of the requirement for a "complex" approval procedure).
So I did not mean the clarity in the specific individual case, but that the legislator defines entire groups of projects which are typically suitable for simplified procedures (because of the relative simplicity of the examination).
For the present request, I see good chances not to have to immediately consult the very greatest oracles
Why didn’t you use an exemption procedure? Was that not a consideration?
I read
The house dates from around 1800.
as a fairly certain indication for "not a development plan area".