Knee wall height in a single-story building

Hello. We currently have a problem. We are supposed to build according to the dimensions of 9x11, with two bay windows on the sides. These do not reach the peak of the roof. Permissible according to the development plan is 1 story. Now our builder says that we can only have a knee wall of 75cm. Is that really the case? The roof pitch is planned at 45 degrees.

There is missing information. Often it is (only) a calculation example, but for that you need numbers. And of course the valid state building code with the full storey specifications. And if you handle a self-drawn section with a set square, you can see for yourself how high the KS may be. Especially at 45 degrees, it is very easy on graph paper. You probably mean dormers when you say bay windows, otherwise it makes no sense.

with two bay windows on the sides. These do not reach up to the peak of the roof.

I suspect that "Friesengiebel" are meant here, and that these do not reach the ridge. Nevertheless, this roof shape is predestined to, in combination with a pitch angle of around 45°, encroach into the calculated "hazard zone" of a full story.

a knee wall of 75cm

... I avoid like the plague: such a knee wall is neither fish nor fowl, it does not fully substitute a short wall (which is the purpose of a knee wall).

Am I a rogue if I further think that a general contractor might be meant by the developer?

Thank you for the initial explanations. The statement about the Friesengiebel and the ridge is correct. We were just sitting at the desk to draw. We haven’t made much progress because of that. If I extend the house with the roof slope, there is no change, right? I mean with regard to the floor area on the ground floor and upper floor. I would have to make the house deeper, right? So, for example, widen the gables by about 1 meter, right? Maybe we’ll also adjust the roof slope a bit.

If I extend the house with the sloping roof

You mean: to extend the rectangular floor plan in ridge direction? - with a gable roof without cross gable this calculation would actually be neutral, here it is a bit more complex.

Maybe we will also adjust the roof slope a bit.

What can you actually adjust? - we still lack bags of information: eaves height, ridge height, their reference height, the roof pitch from/to, permitted roof types, restrictions for roof structures, knee wall height with reference basis, ..., ... What do you actually want to achieve: determine the breakeven point, i.e. get the maximum standing height area while avoiding a full storey?; and would that even have to be: how does it behave with floor area ratio and plot ratio (we don’t even know the absolute area so far, apart from the example of the 99 sqm floor area)?

With us, it was converted into a two-story building by using a simple front pike, knee wall with us 100cm