Is window planning mandatory according to DIN 5034-2021-08?

Our architect believes that the window size must be planned according to DIN 5034-2021-08 (new construction single-family house). This should cost about 3000 EUR, as complex calculation and outsourcing are necessary. How binding is this DIN standard? Would the building application probably still be approved if the brightness (etc.) of the standard is not achieved everywhere?

Would the building application probably still be approved if the brightness (etc.) does not meet the standard everywhere?

The building application does not mention anything about that. As far as I know, the DIN standard is not a legal requirement but a guideline that architects use as a reference. However, I have never seen it applied in single-family homes. So no, the approval of the building application does not depend on that and it is not asked for there.
I would kick out an architect who wants 3k just for that for a single-family home. Especially since any "normal" single-family home doesn't cause any problems anyway.

Thank you. This approximate amount is probably usually charged by companies commissioned for this in order to calculate it correctly. The architect says that he cannot do it himself. The simplified standard has probably been discontinued.

I would be interested to know where the legal basis for the calculation according to the DIN is stated. There are many recommendations in it, such as 10% of the floor area as window area. But I would not know that it is mandatory (unless this has changed recently). Hence the question, where the basis for this is. And then I would also be interested to know why the architect does not base it on the more recent [DIN-EN-17037], which actually replaces the old DIN. Lastly, a note that the exclusive legal obligation is found in the state building code. In Bavaria, see Article 45. There are no further legal obligations. The DIN can be applied voluntarily to increase comfort. Please do not engage with the 3k calculation.

Thank you for your information. I will ask him about the basis. Maybe someone else knows something regarding this.

Maybe someone else knows something about this.

I would be interested as well. I only know such considerations from commercial properties (mainly office buildings), where lighting is a matter of occupational safety and therefore mandatory.