How does it continue? Construction beyond the rear building line

Hello everyone,

I am an absolute beginner when it comes to building a house and now need a little help from the professionals

We have purchased a plot of land that will be fully developed by the end of September. A two-story prefabricated house and a garage with the dimensions shown in the drawing are planned for the plot.

We want to exceed the rear building boundary and, according to the building authority, are supposed to clarify this with the respective neighbors.

How should we proceed best? Everything should go the right way and there should be no unpleasant surprises later?

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Step 1: already had a chat with the neighbor?

Step 2: A beer and a grilled sausage...

The building boundaries are not there without reason. I would reject that as a neighbor. Why are you buying a plot of land if your house does not fit "on it"?

I would also reject that. Especially the neighbor upstairs now gets the garage placed right in front of him and his terrace and parts of his garden are cast into shadow.

With appropriate planning, both the house and the garage can be placed within the building envelope.

I am well aware that these building boundaries were not created out of boredom. Of course, the garage could still be pushed forward; I have already adjusted the ground floor accordingly. In the building area in general, there are occasional exceedances here and there, hence the idea.

Regarding the question why this property?... why not? It largely depends on the location and the price. The selected house would be our current wish and could be realized with an extension beyond the rear building boundary (red triangle), provided the neighbors agree. However, we are also open to other variations.
Currently, the plan is without a basement. Up to 3m or 20sqm, an extension beyond the rear building boundary would be possible, for example, one-story. So, there are several possibilities.