Knee wall at eaves height 3.50m in the development plan

Hello everyone. Maybe the experts here can help me a bit. I am currently getting more involved with the topic of house construction. We have a plot of about 750 sqm in sight. In the development plan it states for eaves height: The eaves height measured at the intersection of the outer edge of the outer masonry with the lower edge of the rafters may be max. 3.50 m above the raw floor of the ground floor. One full storey is allowed. I assume it will be tight with a knee wall?
Further information is:
Floor area ratio 0.3
Floor space index: 0.3
There is no information on the roof shape.
Thanks in advance.

750 sqm times 0.3 is 225 sqm, so you should be able to get enough space on the ground floor to also accommodate a few rooms upstairs in the non-full storey. Let's assume the worst case and consider a roof without any knee wall: then you can take the colloquial name "one-and-a-half storeys" quite literally, meaning you will be able to create about half as much living space in the attic as on the ground floor, thus a maximum of 150 below and 75 above due to the maximum 225 from the 0.3 floor area ratio. The 150 below will translate to a ground area of 180 to 190, so the maximum of the 0.3 ground area ratio is also respected. The measuring point on your ground floor is favorable – other builders struggle with manhole covers or completely different reference heights. From the 350 cm, we subtract 285 cm storey height (from floor to floor), leaving us 65 cm. This is quite a lot for a vacuum knee wall, but in the overall situation I would probably advise knee wall 0 and curb. But even with the mentioned knee wall, you would probably remain below the full storey limit (simplified, about 2/3 or in some federal states also 3/4 as much upstairs as downstairs). One way or another, I see you essentially having to use gable and roof windows for lighting in the attic. Does the development plan say anything about roof extensions ("dormers")?

It's best if you tell me what you actually want to build: how many square meters, and how much of that would fall to the upper rooms?

Yes, thanks first for the information. We are imagining a house size between 150 and 170 sqm. There is nothing specified about roof structures like dormers in the development plan. And what about a recessed top floor?

In the case of a stepped roof, the eaves would not be at 3.50m, right? Usually, inclines that seem too low to you are boxed in. This is usually not a big deal, since the house doesn't differ significantly in price from houses with knee walls (at least that was the case at the time I built). You do save a few bricks. But you have to plan differently - meaning more rooms on the ground floor, which in my opinion is not a big deal either.

In the case of a setback, the eaves would not be at 3.50m, correct?

Presumably, the development plan says nothing about at what setback the wall height of the upper floor would no longer be relevant. However, it would have to affect both eave sides at least. Therefore, a significant gain in space would not be associated with it; on the other hand, it would be more expensive.

Usually, slopes that are too low for you are boxed in. That is usually not a big deal,

Exactly: from the inside, knee wall and dwarf wall are no different here to cause a big issue.