ᐅ Clear stairhead height. What are the regulations?

Hello,

can someone help me with a dispute regarding DIN STANDARD 18065?
The staircase in our house is 100cm (39 inches) wide (single-family house).
I understood the drawing about the clear staircase headroom from the DIN as follows:
On both the right and left sides of the staircase, an area of maximum 25cm (10 inches) measured horizontally from the wall is allowed to be under 2m (6 ft 7 in) in height.
Our builder argues that a staircase in a single-family house is allowed to have a minimum width of 80cm (31 inches); the staircase he planned is 100cm (39 inches). Therefore, he believes he is allowed to recess from the wall by 45cm (18 inches), before the 2m (6 ft 7 in) headroom height must be reached. (It is a shed roof, so the slope of the ceiling only needs to be considered on one side.)
Is that correct?
The relevant sketch in the DIN only states less than or equal to 25cm (10 inches) from the right and left of the staircase (and does not say anything about "depending on the width of the staircase").
Can anyone help here?

Regards
Gerda

Gerda schrieb:
Therefore, he believes that he can recess 45cm (18 inches) from the wall until the 2m (6 ft 7 in) clearance height must be reached.

.. no .. 25 cm (10 inches) + 10 cm (4 inches) = 35 cm (14 inches), with the slope not exceeding 45 degrees .. (the 10 cm (4 inches) result from 100-80/2= 10 cm (4 inches))

Hello,
thank you for your reply.
However, the sketch in the standard (edition 2011-06, page 25, section figure A.8) states: on the right and left sides less than or equal to 25cm (10 inches) and in the middle greater than or equal to 50cm (20 inches).
And this is the sketch for up to 2 dwellings (so also applicable for a single-family house).