Energy expert refuses further support

The classification as renovation came directly from the building authority after several discussions and internal agreements.

I do not see it as the only, but certainly one essential crucial point (and a high probability that another building authority could come to an opposite result). In the present case, if I remember correctly, one could read the "single-family house" as a "detached condominium in an ensemble," which would not be the case in your situation. Referring to the entire WEG, it was therefore arguable here that only an insignificant part was affected by the measure.