Regulations regarding development plans, any experiences?

You are confusing buildable area (floor space index) with the total living area of the ground floor combined with the upper floor/attic (floor area ratio). After all, a few square meters do add up in the attic

That would also be more understandable to me, but according to the land use ordinance, the floor area must be determined according to the external dimensions of the building in all full storeys. And if, according to the development plan, I am only allowed to build one full storey, then this is decisive for me.

You are still allowed to add a roof with living space on top. It just must not become a full storey.

You are still allowed to put a roof with living space on it. It just must not become a full storey

But if I already have to build a full storey of 273 sqm, I no longer need an attic floor.

You don't have to do anything at all. These are threshold values.

You don't have to do anything. These are limit values.

No, according to the development plan, a minimum floor area ratio of 0.35 and a maximum floor area ratio of 0.45 are required. That's what confuses me.

No, according to the development plan, a minimum floor area ratio of 0.35 and a maximum floor area ratio of 0.45 are stipulated. That's what is confusing me.

You posted an excerpt from the development plan. I do not read anything about minimum values, only about lower and upper limits.

Nevertheless, I must admit that I am also confused that the floor area ratio of all full stories is meant.

Haven't you called the building authority today to ask?