Clear stair passage height. What are the regulations?

Hello,

can someone help me with disputes regarding DIN STANDARD 18065.
Our staircase in the house is 100cm wide (single-family house).
I had understood the drawing about the clear stair passage height from the DIN as follows:
On the right and left of the staircase, an area of max. 25cm (measured horizontally from the wall) may be under 2m.
Our builder argues that a staircase in a single-family house may have a minimum width of 80cm; the staircase planned by him is 100cm. Therefore, he believes that he may recess 45cm measured from the wall until the 2m passage height must be reached. (It is a shed roof, so the slope of the ceiling only needs to be considered on one side).
Is this correct?
In the corresponding sketch from the DIN, it only states less than or equal to 25cm from the right and left of the staircase (and nothing about "depending on the width of the staircase").
Can someone help here?

Regards
Gerda

Thus, he believes that he may recess 45 cm from the wall until the 2 m passage height is reached.

.. no .. 25 cm + 10 cm = 35 cm whereby the 45-degree slope must not be exceeded .. (the 10 cm result from 100-80/2= 10 cm)

Hello,
Thank you for the response.
However, the sketch in the standard (edition 2011-06, page 25, section figure A.8) is different; it states: right and left smaller/ equal to 25cm and in the middle greater/ equal to 50cm.
And this is for the sketch for up to 2 apartments (so also for a single-family house).